Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. COMPARISON OF HERITAGE AND MODERN CROP CULTIVARS IN RESPONSE TO IRRIGATION AND NITROGEN MANAGEMENT A thesis presented in partial fulfilment of the requirements for the Degree of DOCTOR OF PHILOS OPHY in Plant Science Institute of Natural Resources Massey University Palmerston North, New Zealand ISAAC RHINNEXIOUS FANDIKA 2012 i ABSTRACT There is a resurgence of interest in heritage crop cultivars (potatoes, squash and yams) in New Zealand because of the premiums farmers get at niche markets. However, a paucity of information in relation to their growth characteristics and resource use efficiency limit successful management of these crops. This research compares the response of different heritage and modern crop cultivars to irrigation, nitrogen (N) fertiliser and canopy management. Some heritage cultivars produced as much marketable yield as modern cultivars while other heritage cultivars had low yields. Modern potatoes were more responsive to irrigation and N than heritage potato crops (collectively known as Taewa). Application of more than 80 kg N ha-1 decreased yield in Taewa (Moe Moe, Tutaekuri) whereas, it increased the yield of modern potatoes (Agria, Moonlight). Full irrigation (FI) increased yield in modern potatoes and Moe Moe. In contrast, Tutaekuri yield was greatest with partial irrigation (PI). FI and 80 kg N ha-1 are recommended for Moe Moe production whereas PI and less than 80 kg N ha-1 are recommended for Tutaekuri. In addition, greater tuber dry matter and low sugar content suggest that Taewa would have better cooking and processing qualities than modern potatoes. Heritage crops required more water than modern crop cultivars because they mature later. There was high ?water use efficiency? in heritage pumpkin squash; high ?irrigation water use efficiency? in modern potatoes and high ?economic water productivity? for heritage potatoes and pumpkin squash. Heritage crop cultivars adapted to water deficit by developing more roots, higher photosynthetic WUE and leaf water potential than modern cultivars. Although total biomass production was similar, heritage crops tended to produce less marketable yield than modern cultivars because of excessive vegetative growth and potato psyllid infestation. Two strategies to manage the canopy and reduce vegetative growth using chlorocholine chloride (CCC) and mechanical topping were developed. Both strategies increased marketable yield in Taewa by 32 - 44%. Application of CCC at 25 and 50 days after emergence (DAE) was recommended for irrigated Taewa, whereas mechanical topping and application of CCC at 25 and 30 DAE were recommended for both irrigated and rain-fed Taewa. The study also observed that potato psyllid need to be controlled up to 170 DAE in Taewa to avoid yield loss equivalent to NZ$10, 485 to NZ$17, 412 per ha. This study contributes to policy on sustainable and improved Maori land use. It can be concluded that premium market prices are important to the success of heritage crops (i.e. to maintain their high ?economic water productivity?) whereas modern crops might use irrigation water more efficiently (i.e. greater ?water use efficiency?). It is evident that heritage crops can be grown successfully, and that on occasions they use valuable resources efficiently. To enhance water use efficiency, management of heritage crops should focus on improving the harvest index. ii iii ACKNOWLEDGMENTS With honour and adoration, I pay tribute to God almighty for his enormous love and care to allow me conclude this thesis successfully. I owe a recognition and respect to scores of people and institutions for their kind assistance at innum erable stages of my PhD studies. I wish to express my heartfelt indebtedness to my Chief Supervisor Professor Peter D Kemp, who gave enthusiastic and motivating leadership and support throughout this project. I also thank Dr James P Millner and Dr David J Horne for mutual and solitary efforts on agronomic and irrigation aspects of this study in their capacity as Co- Supervisors. I also thank Dr Nick Roskruge who gave major contribution and momentum to Taewa or Maori potato and modern potato management. I gra tefully thank the Institute of Natural Resources, especially Mr. Mark Osborn, Mr Chris Rawlings, Steven Ray (PGU), Ian Furkert and Felicity Jackson for their kindness, friendship, provision of up to date equipment and land preparation, photosynthesis measurements, glasshouse experiment, computer work, soil and nitrogen leaching sampling and analysis, and finally sugar determination in potato. Many thanks also go to my fellow postgraduate students: Godwin Rwezaula, Francis Amaglow, Agness Nkhoma , Lawrent Pungulani and Pilirani Pamkomera with whom I shared knowledge, many beautiful moments, friendship and help in many different ways. I thankfully acknowledge NZAID - Commonwealth Scholarship and the International Office at Massey University especially, Sylivia Ho oker, Olive Pimentel, Jamie Hooper and Sue Flyn for the good services they offered me during the administration of the Commonwealth scholarship for me and my family. On the same note, I acknowledge the Malawi Government, especially the Department of Human Resource, A.M Liwonga; The Permanent Secretary for Ministry of Agriculture and Food Security, Dr A.T Daudi; and The Director of Agricultural Research Services, Dr Alfred Mtukuso for nominating me for the Commonwealth Scholarship and offering me leave of a bsence for this study. I gratefully acknowledge my late father and my mother, Etness Fandika, my sisters; Mrs Felia Kaweya, Mrs Lucy Robert and Mrs Fyness Nzunga, and my brothers; Benjamin Fandika, Grant Fandika, Dickson Fandika and Precious Fandika for their moral and financial support beginning from primary school, secondary school and University. Indeed without their support, I could not have had education to all levels. I also acknowledge my extended family members and people from Tchauya Village, T/A N jolomole, Ntcheu for their support to my iv mother and siblings during my absence. At last but not least, my profound gratitude to my wife, Esther Limiton Fandika, my daughters: Fatsani Fandika and Patience Fandika, sons: Rueben Fandika and Kupatsa Fandika who have made my work possible and for bringing our family cheer and happiness. Esther sacrificed her own career to accompany me to New Zealand and without her continuous infusions of love, support, encouragement and above all patience! I just cound not have made it. v DEDICATION This Thesis is dedicated to my late father (Limbikani Fandika) and late brothers (Moses Fandika & Misheck Njunga ). I also dedicate this work to all people of Tchauya Primary School /Village (1979 - 1987) , Chikapa Primary School (1987 - 1988 ) , South Lunzu MCDE (1988 - 1990) , Nyambadwe MCDE (1990 - 1992) , Natural Resources College (1992 - 1994) , Bunda College of Agriculture (1997 - 2002) and Cranfield University, Silsoe , UK (2003 - 2004) who assisted me on my voyage to fulfill this task. What is th e Meaning of Life in a Meaningless World, "Vanity of vanities? (Ecclesiastes 1:1 - 2). The meaning of life is in Christ Jesus "For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them." (Ephesians 2:10). But as many as received him, to them he gave power to become the sons of God, even to them that believe on his name (John 1: 12). vi vii viii ix x TABLE OF CONTENTS COMPARISON OF HERITAGE AND MODERN CROP CULTIVARS IN RESPONSE TO IRRIGATION AND NITROGEN MANAGEMENT ABSTRACT ............................................................................................................................ i ACKNOWLEDGM ENTS ...............................................................................................................iii DED ICATION ........................................................................................................................... v CANDIDATE?S DECLARATION ................................................................................................. vi SUPERV ISOR? S DECLARATION ..............................................................................................viii TABLE OF CONTENTS ................................................................................................................ ix APPENDICES ....................................................................................................................... xvii L IST OF TABLES ........................................................................................................................ xix L IST OF FIGU RES ...................................................................................................................... xxii L IST OF PLATES ...................................................................................................................... xxiv GLOSSARY AND ABBREV IATIONS ...................................................................................... xxv CHAPTER 1 GENERAL INTRODUCTION AND RESEARCH OBJ ECTI VES .................... 1 1.1 Introduction ......................................................................................................................... 1 1.2 Water use efficiency ............................................................................................................ 2 1.2.1 Importance of heritage crops in modern production systems ......................................... 2 1.2.2 Importance of WUE concepts in crop production systems ............................................ 4 1.3 Research hypothesis and Specific objectives ...................................................................... 5 1.4 Thesis outline....................................................................................................................... 6 CHAPTER 2 LITERATURE REV IEW ..................................................................................... 7 2.1 Introduction ......................................................................................................................... 7 2.2 Water use efficiency concept and indicators: key definitions ............................................. 7 2.2.1 Rationale for WUE concepts .......................................................................................... 7 2.2.2 Crop water productivity and crop- water production function ........................................ 8 2.2.3 Water footprint or virtual water content (m 3 tonne- 1 ) of growing crops ....................... 13 2.2.4 Nitrogen use efficiency ................................................................................................. 15 2.3 Soil ?Plant ?Atmospheric Continuum (SPAC) and Physiological WUE ............................ 15 2.3.1 Plant water uptake and soil or root system ................................................................... 15 2.3.2 Evapotranspiration and irrigation requirements ........................................................... 18 2.4 Taewa species and production trend in New Zealand ....................................................... 20 xi 2.5 Strategies and constraints for maximising crop water productivity ................................. 23 2.5.1 Opportunities for maximising WUE in agriculture ...................................................... 23 2.5.2 Water and nitrogen ma nagement in modern potato production ................................... 24 2.5.3 Effects of mechanical and hormonal canopy manipulation on yield and WUE ........... 31 2.5.4 Challenges and limitations to maximisation of WUE in arable crops .......................... 32 2.6 Summary and conclusion .................................................................................................. 34 CHAPTER 3 COMPARISON OF WATER AND NITROGEN USE EFF ICIENCY OF TAEWA AND MODERN POTATO CULTIVARS IN A GLASSHOUSE .................................................................................................. 37 3.1 Introduction ....................................................................................................................... 37 3.2 Material and Methods ........................................................................................................ 38 3.2.1 Location and plant establishment ................................................................................. 38 3.2.2 Treatments and experimental design ............................................................................ 38 3.2.3 Crop physiological and soil moisture measurements ................................................... 40 3.2.4 Tuber yield, water and nitrogen use efficiency ............................................................ 41 3.2.5 Specific gravity and tuber dry matter content .............................................................. 41 3.2.6 Statistic al analysis ........................................................................................................ 42 3.3 Results ......................................................................................................................... 44 3.3.1 Evapotr anspiration and soil moisture content (%) ....................................................... 44 3.3.2 Vegetative growth characteristics in four potato cultivars ........................................... 46 3.3.3 Photosynthetic water use efficiency and gaseous exchange in the glasshouse ............ 49 3.3.4 Tuber yield response to irrigation and N regime in four potato cultivars .................... 53 3.3.5 Water use efficiency and nitrogen use efficiency of four potato cultivars ................... 55 3.3.6 Specific gravity and tuber dry matter content in four potato cultivars ......................... 59 3.4 Discussion ......................................................................................................................... 61 3.4.1 Evapotranspiration and volumetric soil water content ................................................. 61 3.4.2 Vegetative growth characteristics of Taewa and modern potato cultivars ................... 61 3.4.3 Photosynthetic WUE and gaseous exchange in Taewa and modern potato ................. 62 3.4.4 Total tuber yield, water and nitrogen use efficiency .................................................... 63 3.4.5 Specific gravity and tuber dry matter content .............................................................. 65 3.5 Conclusion ......................................................................................................................... 66 xii CHAPTER 4 COMPARISON OF MOD ERN AND HER ITAGE POTATO, OCA AND PUMPKIN SQUASH CULTI VARS? RESPONSE TO IR R IGATION AND RAIN - FED IN THE FIELD ..................................................................... 67 4.1 Background........................................................................................................................ 67 4.2 General materials and methods .......................................................................................... 67 4.2.1 Experimental site .......................................................................................................... 67 4.2.2 Experimental layout and crop management ................................................................. 68 4.2.3 Plot- size and plant spacing ........................................................................................... 69 4.2.4 Fertiliser application and plant protection .................................................................... 69 4.2.5 Irrigation system and irrigation scheduling .................................................................. 70 4.2.6 Morphological and physiological characteristics measurements ................................. 72 4.2.7 Final total yield and yield components measurements ................................................. 75 4.2.8 Determination of efficient water use: key indicators .................................................... 76 4.2.9 Statistical analysis ........................................................................................................ 78 4.3 Results ......................................................................................................................... 78 SECTION 4.3.1 TAEWA AND MODERN POT ATO CULTIVARS? RESPO NSE TO IRR IGATION AND RAIN - FED CONDITIONS .............................................. 80 4.3.1.1 Introduction ................................................................................................................ 80 4.3.1.2 Materials and methods ............................................................................................... 80 4.3.1.3 Results ........................................................................................................................ 80 4.3.1.3.1 Crop evapotranspiration, precipitation and irrigation ...................................... 80 4.3.1.3.2 Volumetric soil water content (%) ................................................................... 81 4.3.1.3.2 Vegetative growth characteristics of Taewa and modern potato cultivars ...... 82 4.3.1.3.3 Photosynthetic water use efficiency and gaseous exchange ............................ 85 4.3.1.3.4 Leaf water potential (?w) ................................................................................ 87 4.3.1.3.5 Dry matter production and partitioning characteristics ................................... 88 4.3.1.3.6 Tuber yield and yield components in Taewa and modern potato cultivars ........................................................................................................... 90 4.3.1.3.7 Water use efficiency for Taewa and modern potato cultivars ......................... 93 4.3.1.3.8 Specific gravity, tuber dry matter content and total sugars ............................. 93 4.3.1.4 Discussion .................................................................................................................. 95 4.3.1.4.1 Vegetative growth characteristics .................................................................... 95 xiii 4.3.1.4.2 Photosynthetic WUE and gaseous exchange of Taewa and modern potato ............................................................................................................... 96 4.3.1.4.3 Leaf water potential of Taewa and modern potato cultivars ........................... 97 4.3.1.4.4 Dry matter partitioning and tuber yield of Taewa and modern potato ............ 98 4.3.1.4.5 Water use efficiency ...................................................................................... 100 4.3.1.4.6 Specific gravity and tuber dry matter content ................................................ 101 4.3.1.4.7 Total sugars ................................................................................................... 101 4.3.1.5 Conclusion ............................................................................................................... 102 SECTION 4.3.2 OCA CULTIVARS? RESPO NSE TO IRR IGATION AND RAIN - FE D CONDITIONS ................................................................................................. 103 4.3.2.1 Introduction ............................................................................................................. 103 4.3.2.2 Materials and Methods ............................................................................................ 103 4.3.2.3 Results ..................................................................................................................... 104 4.3.2.3.1 Crop water use and soil moisture content ...................................................... 104 4.3.2.3.2 Photosynthetic water use efficiency and gaseous exchange .......................... 106 4.3.2.3.3 Tuber growth and development ..................................................................... 108 4.3.2.3.4 Total and marketable tuber yield, yield components and WUE .................... 110 4.3.2.4 Discussion ................................................................................................................ 110 4.3.2.4.1 Crop water use and soil moisture content ...................................................... 110 4.3.2.4.2 Photosynthetic water use efficiency and gaseous exchange .......................... 112 4.3.2.4.3 Tuber formation and growth .......................................................................... 112 4.3.2.4.4 Total tuber yield, marketable tuber yield and tuber yield components ......... 113 4.3.2.5 Conclusion ............................................................................................................... 114 SECTION 4.3.3 M ODERN AND HER ITAGE PUMPKIN SQUASH CULTIVARS? RESPONSE TO IRR IGATION AND RAIN - FED CONDITIONS ................. 115 4.3.3.1 Introduction .............................................................................................................. 115 4.3.3.2 Materials and Methods ............................................................................................. 116 4.3.3.3 Results ...................................................................................................................... 116 4.3.3.3.1 Crop water use and soil moisture content ...................................................... 116 4.3.3.3.2 Pumpkin squash growth and yield components characteristics ..................... 117 4.3.3.3.3 Pumpkin squash fruit size distribution .......................................................... 118 4.3.3.3.4 Pumpkin squash fruit yield and water use efficiency (kg ha - 1 m- 3 ) ................ 119 4.3.3.4 Discussion ................................................................................................................ 121 xiv 4.3.3.5 Conclusion ............................................................................................................... 123 SECTION 4.3.4 COMPARISON OF KEY WATER USE EFF ICIENCY I ND ICATORS FOR HER ITAGE AND MODERN POTATO, PUMPKIN SQUASH AND OCA CULTIVARS ................................................................................ 124 4.3.4.1 Introduction .............................................................................................................. 124 4.3.4.2 Materials and Methods ............................................................................................. 125 4.3.4.3 Results ...................................................................................................................... 125 4.3.4.3.1 Crop water use and total yield summary ....................................................... 125 4.3.4.3.2 Irrigation water use efficiency and water stress index ................................... 126 4.3.4.3.3 Water footprint of growing heritage and modern crop cultivars ................... 128 4.3.4.4 Discussion .................................................................................................................. 132 4.3.4.4.1 Crop water use and total yield production ..................................................... 132 4.3.4.4.2 Irrigation water use efficiency ....................................................................... 133 4.3.4.4.3 Water footprint of growing heritage and modern crop production ................ 134 4.3.4.4.4 Economic water productivity ......................................................................... 135 4.4 Summary and Conclusion ................................................................................................ 136 CHAPTER 5 COMPARISON IN THE FI ELD OF YIELD AND WAT ER USE EFFICIENCY OF TAEWA AND A MODERN POTATO CULTIVAR ....... 139 5.1 Introduction ..................................................................................................................... 139 5.2 Material and Methods ...................................................................................................... 140 5.2.1 Experimental site ........................................................................................................ 140 5.2.2 Experimental design and treatments ........................................................................... 140 5.2.3 Irrigation and crop management ................................................................................. 142 5.2.4 Plot size and plant spacing ......................................................................................... 143 5.2.5 Growth morphological and gaseous exchange characteristics measurements ........... 143 5.2.6 Soil water sampling procedure for nitrate leaching measurements ............................ 144 5.2.7 Tuber yield and biomass production measurements ................................................... 145 5. 3 Results ....................................................................................................................... 147 5.3.1 Crop evapotranspiration and soil moisture content .................................................... 147 5.3.2 Vegetative growth characteristics of Taewa and modern potato cultivars ................. 150 5.3.3 Photosynthetic water use efficiency and gaseous exchange ....................................... 152 5.3.4 Leaf water potential ( ?w) ........................................................................................... 154 5.3.5 Dry matter production and partitioning ...................................................................... 154 xv 5.3.6 Tuber yield and yield components ............................................................................. 158 5.3.7 Water use efficiency, economic water productivity and nitrogen use efficiency ....... 164 5.3. 8 Crop water production function for Taewa and modern potato ................................. 168 5.3.9 Specific gravity and tuber dry matter content ............................................................ 169 5.3.10 Effect of irrigation on nitrate - N concentration and N losses in the soils grown with Taewa and modern potato cultivars .................................................................... 170 5.4 Discussion ....................................................................................................................... 172 5.4.1 Crop water use and soil water content ........................................................................ 172 5.4.2 Vegetative growth and dry matter partitioning characteristics ................................... 172 5.4.3 Photosynthetic water use efficiency and gaseous exchange ....................................... 174 5.4.4 Leaf water potential ( ?w) ........................................................................................... 175 5.4.5 Tuber yield and yield components ............................................................................. 177 5.4.6 Water use efficiency, economic water productivity and nitrogen use efficiency ....... 178 5.4.7 Irrigation water use efficiency ..................................................................................... 179 5.4.8 Specific gravity and tuber dry matter content ............................................................ 180 5.4.9 Ammonium- N and nitrate - N concentration in the soil water under irrigation and rain- fed ....................................................................................................................... 181 5.5 Conclusion ....................................................................................................................... 181 CHAPTER 6 EFFECT OF MECHANICAL AND HORM ONAL CANOPY MANIPULATION ON TAEW A UNDER LIM ITED AND UNL IM ITED WATER AND NITROGE N C ONDITIONS ................................................... 183 6.1 Introduction ..................................................................................................................... 183 6.2 Material and Methods ...................................................................................................... 184 6.2.1 Experimental Site ....................................................................................................... 184 6.2.2 Experimental design and crop management ............................................................... 185 6.2.3 Plot- size and plant spacing ......................................................................................... 186 6.2.4 Plant physiological characteristics and biomass partitioning measurements ............. 186 6.2.5 Potato tuber yield and statistical analyses .................................................................. 188 6.3 Results ....................................................................................................................... 189 6.3.1 Evapotranspiration of Tutaekuri ................................................................................. 189 6.3.2 Volumetric soil moisture (%) ..................................................................................... 190 6.3.3 Photosynthetic water use efficiency and gaseous exchange ....................................... 191 6.3.4 Vegetative plant growth characteristics ...................................................................... 193 xvi 6.3.5 Dry matter production and partition ing ...................................................................... 194 6.3.6 Tuber yield and yield components at final harvest ..................................................... 196 6.3.7 Water use efficiency and irrigation water use efficiency ........................................... 198 6.4 Discussion ....................................................................................................................... 200 6.4.1 Photosynthetic WUE and gaseous exchange .............................................................. 200 6.4.2 Vegetative growth and dry matter production ............................................................ 201 6.4.3 Total tuber yield and yield components ..................................................................... 202 6.4.4 Crop water use, WUE and irrigation water use efficiency ......................................... 205 6.5 Conclusion ....................................................................................................................... 207 CHAPTER 7 GENERAL DISCUSS IO N AND CONCLUS ION .......................................... 209 7.1 Introduction ..................................................................................................................... 209 7.2 Water requirements for studied heritage and modern crops ............................................ 210 7.3 Morphological and physiological characteristics of Taewa ............................................ 211 7.3.1 Vegetative growth characteristics and dry matter partitioning ................................... 211 7.3.2 Photosynthetic WUE and photosynthesis ................................................................... 212 7.3.3 Tuber dry matter and specific gravity ........................................................................ 214 7.4 Tuber yield and yield components for Taewa ................................................................. 215 7.4.1 How can Taewa growers maximise water an d tuber yield ? ...................................... 216 7.5 Key water use efficiency performance indicators ........................................................... 219 7.5.1 Water footprint of growing potato, oca and pumpkin squash .................................... 221 7.5.2 Water use efficiency and crop water production functions in Taewa ........................ 222 7.5.2.1 Water use efficiency benchmarks in Taewa ...................................................... 222 7.5.3 Nitrogen use efficiency benchmarks in Taewa ........................................................... 225 7.6 Comparison of Tutaekuri and Moe Moe Characteristics ................................................. 226 7.7 Economics of irrigation on Taewa ................................................................................... 226 7.8 Practical implications of the study for Taewa growers ................................................... 227 7.9 Conclusion and suggestions for future research .............................................................. 228 7.9.1 Future Research .......................................................................................................... 229 REFERENCES ....................................................................................................................... 231 APPENDICES ....................................................................................................................... 251 PUBLICATIONS ....................................................................................................................... 283 xvii APPENDICES Appendix Page Appendix 3.1 V olumetric soil moisture content (%) in the glasshouse, 2009 ....................... 252 Appendix 3.2 Change of An and gs in potatoes during the growing season in the glasshouse 2009; .............................................................................................. 253 Appendix 3.3 Interaction between potato cultivar, irrigation and N on DMC%. ................... 254 Appendix 3.4 Specific gravity and tuber dry matter content (%) relationship for four potato cultivars grown in glasshouse, 2009 ..................................................... 254 Appendix 4.4.1 Precipitation, irriga tion, deep percolation , soil moisture change, actual evapotranspiration, and crop water use per ha in mm from 10th Nov., 2009 to May, 2010 ........................................................................................... 255 Appendix 4.4.2 Effect of irrigation and cultivars on volumetric soil moisture content (%) in the field, 4th January 2009 to 11th May, 2010 ..................................... 256 Appendix 4.4.3 Photosynthetic WUE and Net Photosynthesis for Taewa and modern potato cultivars under irrigation and rain- fed conditions, 2010 ....................... 257 Appendix 4.4.4 Proportion of dry matter partitioning in four potato cultivars ......................... 258 Appendix 4.4.5 Relationship of number of tuber with mean tuber weight (a) and HI (b) ........ 259 Appendix 4.4.6 Relationships between (a) specific gravity and tuber dry matter content; (b) spe cific gravity and total sugars in potato cultivars ................................... 260 Appendix 5.1 V olumetric soil moisture content (%) after 76 DAP , 2010/ 2011 .................... 261 Appendix 5.2 Interaction between potato cultivars and water regime on plant height (a), stems per plant (b), number of branches per plant (c) and interaction between potato cultivars and N on stems per plant (d) .................................... 263 Appendix 5.3 Interaction between water regime*cultivar (a) and cultivar * nitrogen (b) on Tomato/ Potato psyllid infestation. .............................................................. 265 Appendix 5.4 Potato tuber yield- water relationship (a- c) ..................................................... 266 Appendix 6.1 Proportion of dry matter partition to leaves, stems, roots and tubers in Tutaekuri under different nitrogen and canopy manipulations ........................ 268 Appendix 6.2 The relationship of gaseous exchange parameters in Tutaekuri ...................... 268 Appendix 7.1 Daily evapotranspiration during the two growing seasons, October 2009 to June 2010 and October 2010 to April, 2011 ........................................... 269 Appendix 7.2 Difference in Taewa tuber yields between two seasons (2009-2010 and 2010-2011) under same water regimes ....................................................... 270 Appendix 7. 3 Spray schedule and type of pesticides used in 2010/ 2011 .......................... 271 xviii Appendix 7. 4 Total water footprints of growing Taewa and modern potato cultivars under different irrigation regimes, 2010/ 2011. Error bar represent ?SEM. ......................................................................................................... 272 Appendix 7. 5 Optimal WUE benchmarks in Taewa and modern potato based on 2009- 2010 and 2010- 2011 studies ....................................................................... 273 Appendix 7. 6 (abcd) Marginal productivity of Taewa and modern potato as affected by amount of N and water regime ............................................................... 274 Appendix 7.7 The relationship between total tuber and specific gravity (SG) and tuber dry matter content (DM %). ........................................................................ 276 Appendix 7.8 The economic feasibility of Taewa in relation to irrigation investments ... 277 xix LIST OF TABLES Table Page Table 3.1 Mean potato seed tuber weight (g), days to emergence, flowering, disease scores at 0- 5 scale and leaf features ......................................................................... 46 Table 3.2 Potato characteristics on number of stems per plant, plant height (cm) and stem diameter (mm) in the glasshouse, 2009 ............................................................ 48 Table 3.3 Photosynthetic WUE (PWUE) and gaseous exchange in four potato cultivars in the glasshouse, 2009 .............................................................................................. 52 Table 3.4 Photosyntheitic WUE relationship with An, T and gs, leaf temperature (LT), Ci, leaf VPD in four potato cultivars ......................................................................... 53 Table 3.5 Yield response to irrigation and nitrogen regime in four potato cultivars under glasshouse conditions. ................................................................................................ 54 Table 3.6 Water use efficiency (WUE), nitrogen use efficiency (NUE) and visual disease scores in four potato cultivars. .................................................................................... 58 Table 3.7 Specific gravity and tuber dry matter content of four potato cultivars in glasshouse experiment ............................................................................................... 60 Table 4.1 Soil chemical characteristics: pH, nitrogen (N), Olsen phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na) and cation exchange capacity (CEC) for the site as of 10th November, 2009 ........................... 68 Table 4.1.1 Vegetative growth and yield component characteristics of Taewa and modern potato cultivars under irrigation and rain- fed conditions in 2010 ............................. 83 Table 4.1.2 Average leaf features of Taewa and modern potato cultivars under irrigation and rain- fed condition, 2009/ 2010 ............................................................................ 85 Table 4.1.3 Gaseous exchange in Taewa and modern potato cultivars under different water and nitrogen regimes under field conditions, 2009/ 2010 ................................ 86 Table 4.1.4 Effect of water regimes on leaf water potential (bars) in four potato cultivars, 2009/ 2010 .................................................................................................................. 88 Table 4.1.5 Effect of water regimes on amount of leaves, stems, roots, tubers and total biomass on dry matter basis per plant (g), in four potato cultivars, 2009/ 2010 ........ 90 Table 4.1.6 Yield and yield components for Taewa and modern potato cultivars under irrigation and rain- fed conditions, 2009/ 2010 ........................................................... 92 Table 4.1.7 Effect of water regime and cultivars on total sugars, percentage of freeze- dried matter, specific gravity and dry matter content, in 2009/2010 gr owing season ........................................................................................................................ 95 xx Table 4.2.1 Photosynthetic water use efficiency and gaseous exchange in two oca cultivars under irrigation and rain- fed conditions ................................................... 107 Table 4.2.2 Total yield, yield components and WUE for oca under irrigation and rain- fed conditions, 2009/2010 ............................................................................................. 111 Table 4.3.1 Growth and fruit yield components characteristics, total and marketable fruit yield, HI and WUE for Buttercup squash and Kamokamo ..................................... 120 Table 4.4.1 Irrigation Water Use Efficiency, drought intensity index , geometrical yield mean and percentage reduction in heritage and modern crops cultivars, 2010 ....... 127 Table 4.4.2 Consumptive and total water footprint of growing potato, oca and pumpkin squash crop cultivars on total yield (m3 ton. - 1) in New Zealand, 2009/ 2010 ......... 129 Table 4.4.3 Economic water productivity (NZ$) on marketable yield basis in heritage and modern crop cultivars under irrigation and rain- fed conditions ....................... 131 Table 5.1 Soil chemical properties at the beginning of experiment, October, 2010 ............... 140 Table 5.2 Precipitation; irrigation; deep percolation; soil moisture change ; actual evapotranspiration; and crop water use from 27th October, 2010 to 12th April, 2011 ............................................................................................................... 148 Table 5. 3 Vegetative growth characteristics and potato psyllids scores at 110DAE and 140DAE in three potato cultivars, 2010/ 2011 ......................................................... 151 Table 5.4 Photosynthetic WUE, net photosynthesis , stomatal conductance, transpiration, and internal carbon concentration in Taewa and modern potato cultivars under different water and N regimes at 90DAE ....................................... 153 Table 5.5 Effect of water and N regimes on leaf water potential (bars) in Taewa and modern potato cultivars, 2010/ 2011 ....................................................................... 154 Table 5.6 Effect of water and nitrogen regimes on leaf, stem, root, tuber and total biomass on fresh and dry matter basis per plant (g) in three potato cultivars, 2010/ 2011 ................................................................................................................ 156 Table 5.7 Effect of irrigation and N regimes on tuber yield (t ha - 1) and yield components in Taewa and modern potato cultivars, 2011 ...................................... 159 Table 5.8 Water use efficiency, nitrogen use efficiency and economic water productivity for Taewa and modern potato cultivars, 2010/ 2011 ........................... 166 Table 5.9 Comparison of irrigation water use efficiency, drought intensity index, yield geometrical mean and yield % reduction in Taewa and modern potato, 2010/ 2011 ................................................................................................................ 169 Table 5. 10 Tuber dry matter (DM %) and specific gravity for Taewa and Agria, 2011 ........... 169 Table 5.11 Effect of irrigation on nitrate - N concentration in the soils grown with Taewa and modern potato cultivars .................................................................................... 171 xxi Table 6.1 Potential crop evapotranspiration, precipitation, irrigation, deep percolation , soil moisture change, actual evapotranspiration in mm, per crop stage of Tutaekuri ................................................................................................................. 189 Table 6.2 Effect of leaf area manipulation, water and nitrogen regimes on gaseous exchange in Taewa cultivar Tutaekuri ..................................................................... 192 Table 6.3 Effect of leaf area manipulation on vegetative plant growth characteristics in Tutaekuri, 2010/ 2011 .............................................................................................. 193 Table 6. 4 Effect of leaf area manipulation on dry matter production and partitioning per plant in Maori potato cultivar, Tutaekuri, 2011 ................................................ 195 Table 6.5 Tuber per plant, mean t uber weight (g), total tuber yield, biomass, total biomass and final HI for Tutaekuri under different water and N regimes ............... 197 Table 6.6 Effect of canopy manipulation on crop water use ; water use efficiency and irrigation water use efficiency for Tutaekuri, 2011 ................................................. 199 xxii LIST OF FIGURES Figure Page Figure 3.1 Layout of planting bags in the glasshouse ...................................................................... 38 Figure 3.2 Total irrigation accumulated after planting in the glasshouse ....................................... 43 Figure 3.3 V olumetric soil moisture content (%) during the experiment period ............................ 44 Figure 3.3 Photosynthetic WUE for different potatocultivars*D AE ............................................... 48 Figure 3.4 Interaction between irrigation, nitrogen and potato cultivars on A n in the glasshouse ...................................................................................................................... 49 Figure 3.5 Interaction between cultivars, irrigation and nitrog en regime on total tuber yield ............................................................................................................................... 54 Figure 3.6 Interaction between cultivars, irrigation and nitrogen regime on WUE (g/ l ) ............... 55 Figure 3.7 Interaction between cultivars, irrigation and nitrogen regime on nitrogen use efficiency (NUE) (kg/gN) ............................................................................................... 56 Figure 4.1 Schematic diagram of the 1st field experiment layout .................................................... 71 F igure 4.1.1 Cumulative rainfall, potential crop evapotranspiration, monthly average maximum and minimum temperatures for the experimental site, from Nov . 2009 - June 2010 .............................................................................................................. 81 Figure 4.1.2 Volumetric soil moisture (%) change in Taewa and modern potato under irrigation and rain- fed conditions. .................................................................................. 82 Figure 4.1.3 Interaction between cultivars and water r egime on total tuber yield. ............................. 93 Figure 4.2.1 Soil moisture content change during the growing season. ........................................... 105 Figure 4.2.2 Potential and Actual crop water use (mm) under rain- fed and full irrigation for oca, 2009/ 2010 .............................................................................................................. 105 Figure 4.2.3 Oca tuber growth rate (g/day) and (b) tuber biomass (g/plant) at different sampling dates on fresh weight basis. .......................................................................... 109 Figure 4.3.1 Potential and actural crop water use (mm) under rain- fed and full irrigation for pumpkin squash, 2009/ 2010. ........................................................................................ 116 Figure 4.3.2 Volumetric soil Soil moisture measurements corresponding to periodical precipitation (mm) and temperature , 2009/ 2010. ......................................................... 117 Figure 4.3.3 Change of LAI in Buttercup squash and Kamokamo during the growing season ............................................................................................................................ 118 Figure 4.3.4 N umber of size distribution (%) for irrigated and rain - fed Buttercup squash and Kamokamo. ............................................................................................................ 122 xxiii Figure 4.4.1 Crop coeficients and maturity period for modern potato, Taewa, oca and pumpkin squash, 2009/ 2010 ........................................................................................ 128 Figure 5.1 Schematic diagram for the field layout of Experiment 3 for irrigation and nitrogen treatments of Taewa and modern potato cultivars ........................................ 141 Figure 5.2 Cumulative rainfall (mm), potential crop evapotranspiration (mm), monthly average maximum temperature and minimum temperature from Oct ., 2010 - April, 2011 .................................................................................................................... 147 Figure 5.3 Change in volumetric soil moisture content (%) for (a) each cultivar and (b) water regime overtime. ................................................................................................. 149 Figure 5.4 Interaction between potato cultivars and water regime (a); and interaction between potato cultivars and nitrogen (b) on HI% during biomass sampling .............. 157 Figure 5.5 (a) Interaction between water regime*cultivar; (b) interaction between cultivar * nitrogen, on number of tubers per plant: .................................................................... 160 Figure 5.6 Interaction between nitrogen and potato on mean tuber weight (g). ............................. 161 Figure 5.7 Interaction between water regime and cultivar (a), and nitrogen and potato cultivars (b) on total tuber yiel d. .................................................................................. 162 Figure 5.8 Interaction between cultivars, irrigation and nitro gen regime on total tuber yield. ............................................................................................................................. 163 Figure 5.9 Interaction between water regime, nitrogen and potato cultivars on final HI. ............. 164 Figure 5.10 Interaction between cultivars, irrigation and nitrogen regime on WUE . ...................... 165 Figure 5.11 Interaction between cultivars, irri gation and N regime on EWP (NZ$m - 3 ). ................. 167 Figure 5.12 Interaction between cultivars, irrigation and N regimes on NUE. ............................... 167 Figure 5.13 Relationship between photosynthetic WUE and Ci (a) and between net photosynthesis (An) and gs (b) in potato cultivars ....................................................... 176 Figure 6.1 Schematic diagram for Field Experiment 4 on canopy manipulation ........................... 187 Figure 6.2 Change in volumetric soil moisture (%) during the growing season in Tutaekuri, 2010/ 2011. ................................................................................................... 190 Figure 6.3 Interaction between water regimes and canopy manipulation on total yield. ............... 198 Figure 6.4 Interaction between water regime and canopy manipulation on water use efficiency ...................................................................................................................... 206 Figure 7.1 Average numbers of potato psyllids, per trap monitored in Manawatu region, during the 2009/ 2010 and 2010/ 2011 growing season???? ............................... 219 xxiv LIST OF PLATES Plate 3.1 Measurement for specific gravity for Moe Moe, Tutaekuri and Agria tubers ............... 43 Plate 4.1 Irrigation and heritage and modern crop cultivars layout at field level in 2009/ 2010 ...................................................................................................................... 79 Plate 4.2 Fresh biomass partitioning into leaves, stems, tubers and roots in two Taewa and two modern potato cultivars (2010) ............................................................ 89 Plate 4 3 Pumpkin squash fruit size distribution ........................................................................ 119 Plate 5. 1 Gaseouse exchange and Leaf water potential measurements ...................................... 143 Plate 5.2 Outlook of irrigated Moe Moe and Tutaekuri potatoes in 2010/2011 season ............... 146 Plate 5.3 Potato pysllids symptoms in Agria, Moe Moe and Tutaekuri, 2011 ........................... 152 Plate 6.1 Mechanical canopy topping in Tutaekuri, Solanum tuberosum ssp. Andigena in 2011 ......................................................................................................... 188 xxv GLOSSARY AND ABBREVIATIONS ANOVA Analysis of variance An Net photosynthesis Ca Calcium CCC Chlorocholine choline, CWP Crop water productivity CWU Crop water use or consumptive water use oC Degree centigrade CEC Cation exchange capacity Ci Internal carbon concentration DAE Days after emergence DAP Days after planting DII Drought Intensity index DM Dry matter content EWP Economic water productivity ET c Crop evapotranspiration ET o Reference evapotranspiration FI Full irrigation GLM General Linear Model GM Geometric mean gs Stomatal conductance HI Harvest index % IWM I International Water Management Institute IWUE Irrigation water use e fficiency Kg ha - 1 Kilogram per hactare Kg ha - 1 m- 3 Kilogram per hactare per cubic meter K Potassium Kc Crop coefficient LAI Leaf area index LDMC Leaf dry matter content LSD Least Significant Difference LT Leaf temperature MAFF Ministry of Agriculture, Forestry and Fisheries MRZ Maximum root zone xxvi MAD Maximum allowable deficit m3 ton- 1 Cubic meter per tonne Mg Magnesium N Nitrogen Na Sodium NUE Nitrogen use efficiency NH 4 + -N Ammonium-Nitrogen NO 3 - -N Nitrate -Nitrogen NPV Net present value PAR Photosynthetically active radiation PRD Partial root-zone drying PI Partial irrigation PR Percentage reduction PWUE Photosynthetic water use efficiency Pe Rain-fed P Phosphorus RCBD Randomised complete block design SAS Statistical Analysis System software SEM? Standard error of mean SG Specific gravity SLA Specific leaf area SPAC Soil ?Plant ?Atmospheric Continuum SMD c Critical soil moisture deficit SWC Soil water content T Transpiration rate t ha- 1 Tonnage per hectare TDR Time-Domain Reflectometer URI Uniform variable irrigation WF Water footprint, WUE Water use efficiency, VPD Leaf vapour pressure deficit VRI Variable rate irrigation VWC Virtual water content 1 CHAPTER 1 GENERAL INTRODUCTION AND RESEARCH OBJECTIVES 1.1 Introduction Irrigation is very important to New Zealand in relation to drought or climate variability , and for ensuring that crops meet market specifications (MAF, 2002 ). New Zealand agriculture consumption of freshwater resources is 77%; this is just above the global average of 70% (Ministry for the Environment, 2006, New Zealand Government, 2000) . The irrigated area has increased from 470, 000 to 750 000 ha . The dairy industry has the largest irrigated area, followed by cereals and vegetables (MAF, 2004a; New Zealand Statistics, 200 9) . Of the row crops, w heat ( Triticum aestivum), barley ( Hordeum vulgare), peas (Pisum sativum), potato ( Solanum tuberosum) ryegrass (Lolium multiflorum) and white clover seed ( Trifolium repens ) (MAF, 2004a) are predominantly grown with irrigation. New Zealand is now considered to be one of the countries with high agricultural water use ( Clothier et al., 2010). Irrigated farm area and agricultural water consumption are increasing by 5% per annum. Agricultural water consumption is expected to double by 2013 (MAF, 2004b) because of anticipated issues around global food security , population increases, urbanization and climate change (S IW I et al., 2005; Fowler, 1999; Kevin, 2001) . As a consequence, surface and groundwater withdrawal and crop evapotranspiration, in addition to environmental pollution from fertilisers and pesticides, are accelerating (Francis et al., 2003). In general terms, f reshwater is sufficient in New Zealand ; however, the agriculture sector faces water scarcity at certain times due to high pumping cost (IW M I, 2000, 2002) and environmental degradation in its bid for crop diversification and intensification (Francis et al., 2003) . W ater scarcity and environmental degradation are reducing the sustainability and profitability of irrigated crops (MAF, 20 04b). In this situation, growers need to allocate water to crops which have a comparative advantage in water use and also premium national or global market prices (McLaughlin, 1985) . Application of the concept of water use efficiency ( WUE) can benefit farmers in resource use and profit optimization in New Zealand ( Howel l, 2001; Ford et al., 2009) . CHAPTER ONE Introduction 2 1.2 Water use efficiency The Ministry of Agriculture Forestry and Fisheries (MAFF) strategic plan for New Zealand agriculture considers improved WUE to be the key to sustainable development (Ford et al., 2009; Martin et al., 2006). Water use efficiency is one of the five physical indicators (energy, solid waste, WUE, greenhouse ga s and ozone layer depletion) of a sustainable environment (Miskell, 2009). The significance of WUE primarily lies in sustainable water and nutrient use whilst preserving the quality of the aquatic environment. Water use efficiency is both a generic and specific term used for expressing sparing water use in agriculture, at plant level and in the field (Wise et al., 2011; Howell, 2001) . In specific terms, WUE is defined as the quantity of crop yield (kg) per volume of water (m 3 ) used for production ( Howell, 2001) . I n generic terms, WUE relates to maximising the returns from water resources, whilst minimising negative environmental effects ( Wise et al., 2011). Water use efficiency stud ies are essential in New Zealand agriculture to sustain the remarkable increases in irrigation and fertilizer use observed between 1960 to 2009 (M acLeod et al., 2006; New Zealand Statistics, 2009). The focus of this thesis is on WUE of heritage species with novel value in a niche market in the cultural economy of New Zealand (Roskruge, 199 9). 1.2.1 Importance of heritage crops in modern production systems A heritage crop in this thesis is defined as a crop that Maori 1 people inherited from other parts of the world through importation during their migration or those adopted from early European settlers. These crops were traditionally produced in Maori agriculture (Roskruge, 1999) . The heritage crops which migrated with Maori are: kumara ( Impomea batatus ); paper mulberry ( Broussonetia papyrifera) , taro ( Colocasia antiquorum), gourd ( Lagenaria vulgaris ) and yam ( Dioscorea spp). Taewa or Maori potato was adopted from European settlers though it i s orally argued that Maori had some potato varieties in pre- European time (Roskruge, 1999). Taewa ( Solanum tuberosum L., Solanum andigena Juz & Buk.) and heritage pumpkins, Kamokamo ( Curcubita pepo Linn) have been used by Maori for over 200 years (Roskruge, 1999 ) . 1 Maori are the indigenous Polynesian people of New Zealand . CHAPTER ONE Introduction 3 The industry around potatoes, including potato breeding programs, has focused on producing more within a short period over slow producers like heritage crops. However, heritage crops contain many traits (e.g taste) that could be advantageous. Heritage crops are worthy of scientific investigation because most of them (e.g Taewa) have superior flavor, texture or colour and health benefits (Singh et al., 2008; Lister, 20 01); heritage crops increase biodiversity into agriculture; most heritage crops are self ? selected, hence have potential to withstand biotic and abiotic stresses and easily regenerate from seed or tuber seed (Roskruge, 2010 ) . A scientific investigation of heritage crops may also reinvigorate Maori agriculture where a focus is less . It is claimed that heritage crop varieties endure partial water and nitrogen deficits (Siddique et al., 1990a; Zebarth et al., 2008) . Therefore, heritage crops with high economic value have the potential to minimise the water footprint of agriculture, whil st optimising the economic benefits (McLaughlin, 1985). In other words, heritage crop cultivars in New Zealand offer the opportunity for low water use , high nutrition and ?novel? value. Meanwhile, premium prices are offered for Taewa and Kamokamo in New Ze aland (Hayward, 2002; Lambert, 200 8; McFarlane, 2007) . Taewa attracts premium prices due to their novel table value as well as for their cultural value (McFarlane, 2007) . G rowers? interest in these heritage crops (ie Taewa) and other Southern America native crops have now increased, due to a niche domestic market and the cultural economy of New Zealand (Hayward, 2002; McFarlane, 2007 ) . Consumer demand for yellow- flesh, purple skin, red flesh or multi - coloured native potato varieties from South America is also high in the USA (Voss et al., 1999) and Europe, due to their natural flavour (Walker, 1996) . M odern potatoes ( Solanum tuberosum L.) and modern pumpkins known as B uttercup squash (C ucurbuta maxima Duchesne) are typically produced on a large scale for conventional and export markets. Modern potato is classified as the New Zealand?s highest exported processed fresh vegetable and it is generally used for domestic consumption, either as a table or processed potato. The level of exports of B uttercup squash has also increased above that of crown and heritage pumpkin know n as Kamokamo cultivars . Buttercup squash is the fourth largest export horticultural crop, behind kiwifruit, apples and onions (Grant, 1989; Perry et a l., 1997) . CHAPTER ONE Introduction 4 Both modern and heritage crop cultivars have traits related to their yield, morphological and physiological characteristics that will affect the efficiencies with which they use water and nutrients (Abeledo et al., 2011; Feil, 1992; Koc et al., 2003 and Siddique et al., 1990a, 2001). Appropriate water and soil management could possibly reduce the difference in potential yield between modern and heritage crop cultivars (Abeledo et al., 2011). H owever, it is not known whether low yields in heritage cultivars in New Zealand are the result of inappropriate soil and water management, or if genetic traits severely limit yield potential. The majority of heritage crops, whether under rain- fed or irrigation, are produced without consideration of the physical, economic and environmental returns per amount of water used. The New Zealand irrigation sector attempts to reduce inefficiency by regulating application rates (Thomas et al., 2006) through improved system design (He dley et al., 2009a) and irrigation training. In addition, g rowers need to be able to use water resources prudently by selecting suitable cultivars, in order to maximise yields and returns . 1.2.2 Importance of WUE concepts in crop production systems G rowers of standard and heritage crops in New Zealand are more concerned with the effectiveness of irrigation (i.e increased yield) , rather than its efficiency (MAF, 2002, 2004a). W ater use efficiency concepts are restricted by a lack of information on thei r relationship to agronomic performance. W ater use indicators, such as WUE (Howell, 2001; Perry, 2007) , economic water productivity ( Molden et al., 2001; Barker et al., 2003) , irrigation water use efficiency (Howell, 2001) and water footprint or virtual water content of crops (Hoekstra et al., 2007) are likely to be come very important in future. They are likely to impact on future market access , the prices grower receive and water conservation programs. The physiological and morphological characteristics of heritage crops along with modern crops have not been sufficiently studied in New Zealand. T he FAO office in the Asian and Pacific region has ranked research on heat or drought tolerance of potato cultivars, potato with high dry matter and low reducing sugar content (Pandey, 2008) along with efficient water management (Clothier et al., 2010), as priority research areas. The objective of this research was to compare the growth patterns and WUE of different heritage and modern crop cultivars in response to irrigation, nitrogen and canopy management. CHAPTER ONE Introduction 5 1.3 Research hypothesis and Specific objectives The general research question posed was: ?What is the impact of irrigation and nitrogen on heritage crop cultivars, compared to modern crop cultivars, in relation to growth patterns, yield, environment and economic value per water used? ? The specific objectives of this study were: 1. To compare water and nitrogen use efficiency in Taewa and modern potato cultivars subjected to different levels of irrigation and nitrogen, in the glasshouse. 2. To compare key WUE indicators ? irrigation water use efficiency, economic water productivity and water footprint ? of heritage and modern potato, oca and pumpkin squash cultivars, under different soil moisture regimes, in the field. 3. To investigate the effect of irrigation and nitrogen management on Taewa yields, in addition to physiological characteristics, total sugars, tuber dry matter content, residual nitrogen leaching patterns, specific gravity and water use efficiency, compared to modern potato cultivars, in the field. 4. To improve the yield and WUE of a Taewa cultivar, Tutaekuri ( Solanum ssp. andigena), using hormonal and mechanical leaf canopy manipulation, under limited and unlimited water and nitrogen environment, in the field . 5. To compare the economic feasibility of growing Taewa and modern potato cultivars using small scale irrigation. CHAPTER ONE Introduction 6 1.4 Thesis outline Draw attention to emerging issues in heritage and modern crop cultivars in New Zealand , in relation to efficient resource use. The hypothesis and specific obj ectives of this thesis are established. Chapter 1 Introduction & Research Objectives Water saving concept is reviewed in the context of soil - plant- atmospheric continuum, the key indicators for WUE, strategies and constraints for maximis ing crop water productivity in potato and a range of arable crops Chapter 2 Literature Review Chapter 3 Glasshouse experiment Chapter 4 Response of modern and heritage potato, oca, and pumpkin squash to irrigation Chapter 5 Taewa and Agria response to irrigation & N in the field Chapter 7 General Discussions & Conclusion Chapter 6 Canopy manipulation Water and nitrogen use efficiency in Taewa and modern potato cultivars are measured and compared in the glasshouse. Planting bags are used to easily control water and N resource use. The effect of rainfall and irrigation are compared between or within modern and heritage potato, pumpkin squash and oca cultivars on yield, morphological or physiological characteristics and WUE, in the field. The effects of irrigation and N regimes on tuber yield; photosynthetic water use efficiency; specific gravity; and water use efficiency, are compared between Taewa and modern potato, Agria , in field. The effect of irrigation and N on nitrate concentration in soil water grown to Taewa and modern potato is also discussed. The effects of leaf canopy topping and growth regulator foliar spray on Taewa ( Solanum ssp. andigena) under limited and unlimited water and N are discussed. This chapter discusses the findings with reference to literature and economic feasiblity as well as making conclusions and recommendations on the implications to New Zealand and projection of future research are presented. CHAPTER THREE Glasshouse Study 7 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction The scope of this review is in four thematic areas: (i) potential WUE indicators ? key definitions and typical WUE, for a range of arable crops under rain- fed and irrigation; (ii) Soil?Plant ?Atmospheric Continuum (SPAC) and physiological mechanisms of WUE in crops; (iii) Taewa species and p roduction trends in New Zealand and (iv ) strategies and constraints for maximising agronomic WUE in arable crops. Since a general summary of a WUE topic would be exceedingly broad to attempt here, the review focuses on potato ( Solanum tuberosum ), whilst oc a ( Oxalis tuberosa) and pumpkin squash (C ucurbita spp.) are included within Chapter 4. Considering that the benefits of irrigation are dependent on climate and the nature of the production system, this research is specific for New Zealand. However, the res earcher has examined the literature on other regions in the world, in order to understand and obtain a ?picture? as to how potato performs in other climate zones, as a result of the limited information available within the WUE field in New Zealand. 2.2 Water use efficiency concept and indicators: key definitions 2.2.1 Rationale for WUE concepts Smith ( 2000) concluded that agricultural w ater- saving strategies (water saving crops, fertilisation and deficit irrigation), which have demonstrated a great po tential to improve water conservation, need to be embraced. Key indicators within such a framework of WUE are : crop water productivity and yield response factors, k y (Kassam et al., 2001) ; economic water productivity (Molden et al., 20 01); water footprint or virtual water content (Hoekstra et al., 2007) ; and irrigation water use efficiency concepts (Howell, 2001) . These indicators are widely assessed as being the tools for attaining water security and efficient water use, in addition to connecting water consumption patterns and their impact on water resources and the environment (Hoekstra, 200 3; English et al., 1996) . Hedley et al. (2009b) also refer to irrigation water use efficiency ( IWUE ), CHAPTER TWO Literature Review 8 cost of saving, energy used, virtual water content and nitrate leaching as key generic WUE indicators in assessing irrigation performance in New Zealand. Agricultural water saving tools are an essential means of appraising how crops convert water to biomass. These tools also guide on how water can be efficiently and effectively used, by utilising different technologies, at various locations and periods, during agriculture operations (Renault, 2002; Zimmer et al., 2003) . Henceforth, WUE indicators can help to identify crops with a comparative advantage (at different locations), thereby contributing to global water use efficiency. However, there are conflicting views on WUE concepts. S ome scientists argue that the concept of WUE does not show the actual economic value of the water saving or loss (Zoebl, 2006) ? and sometimes the results are contradictory (Zwart et al., 2004) ? whilst the water footprint calculation has been accused of being based only on hypothetical crop and water usage ( Maes, 2009 ) . 2.2.2 Crop water productivity and crop-water production function 2.2.2.1 Crop water productivity (kgha mm - 1 ) W ater use efficiency as a specific term, as per Howell?s (2001) review, is also refered to as crop water productivity (CWP) ( Kassam et al., 2001; Zwart and Bastiaanssen, 2004 ) . Crop water productivity provides a measure of appraising agronomic mechanisms (variety selection, irrigation and fertilisation strategies), as efficient options for agricultural water management. F armers and agronomist also define CWP as the ability of a crop to transform available water (through rainfall, irrigation and the contribution of soil water storage) into economic crop biomass yields (kgha - 1 m3 or kgha - 1 mm ) (Howell, 2001; Perry, 2007). Water use efficiency as a specific term can also be defined in terms of crop photosynthetic capacity, per unit of plant transpiration, thus photosynthetic water use efficiency (photosynthetic WUE) (Xu & Hsiao, 2004) . Kijne et al. (2003) indicated that CWP improves, through mor e crops being produced per amount of water, or by raising crop yields per unit of water consumed. Scientists have also pointed out that CW P, based on biomass yield, is more constant than photosynthetic WUE, because the later varies with CO 2 levels and environmental factors (Xu & Hsiao, 200 4). CHAPTER TWO Literature Review 9 The attainment of water- saving, through the enhancement of output per water input, is achieved with a restricted water supply (Sander et al., 2004), whilst the lat ter is achieved by optimising harvest index per water consumed (Siddique et al., 2001) . 2.2.2.1.1 Typical crop water productivity for a range of crop categories Typical CWP, for a range of crop categories, varies with crop or cultivar, management system, year or location and part of the harvested crop (Nielsen, et al., 2005, 2006) . Crop water productivity, based on total yield biomass, was reported as being the highest in crops with low evaporative demand: and lowest in grain crops in the USA, according to Nielsen et al. (2006). Forage crops had the hig hest CWP of 14.5 kgDMha - 1 mm- 1 , with a decline to 4.2 kgDMha - 1 mm- 1 in oilseeds and 2.8 kgDMha - 1 mm- 1 , respectively, in small grain legumes, whether grown in rotation or continuously ( Nielsen et al., 2005). In another similar study conducted in Australia, CWP for forage maize crops was between 38 and 58 KgDMha - 1 mm- 1 for irrigation water use and 28 KgDMha - 1 mm- 1 and 34 KgDMha - 1 mm- 1 for total water use, which was higher than for other forage crops (Greenwo od et al., 200 4). It was also found that CWP amongst forage crops was affected by climate, where cool season grasses had lower CWP, compared to tropical grasses. The CWP of tropical grasses ranged between 21 to 43 kg ha mm - 1 and 12 - 13 kgDMha - 1 mm- 1 under rain- fed and irrigated conditions, respectively. The CWP of cool season grasses ranged between 13 - 16 and 19 - 35 kgDMha - 1 mm- 1 under rain- fed and irrigated conditions, respectively (Callow et al., 2004). Nitrogen was also report ed to have increased CWP, from 6 and 13.9 kgDMha - 1 mm- 1 to 22.6 kgDMha - 1 mm- 1 with 0 kg Nha - 1 and 225 kg Nha - 1 , respectively, in cool season grasses (Power, 1984). Among forage crops, s orghum and maize , ( C4 plants and tropical forages) maximise d CWP for the summer season, together with one temperate grass: annual ryegrass (Callow et al., 2004). The world?s major food crops are also reported to have high CWP, at the forage biomass, compared to tuber or grain biomass (Anderson et al., 2003) . The CWP for the forage biomass increases with old cultivars compared to modern cultivars (Siddique et al., 2001), because modern cultivars were either bred for high CWP or NUE (Zebarth et al., 2008) . Crop water productivity for wheat grain is 5.2 ? 10.8 kgha - 1 mm- 1 and 23.5 ? 28 kgDM ha mm - 1 for wheat forage biomass in China (Zhang et al., 1999; Zhang et al., CHAPTER TWO Literature Review 10 2005). However, a high CWP range of 4.8 - 12.1 (kgha - 1 mm- 1 ) for grain and 16.1 ? 37 kgDM ha mm - 1 for forage biomass has been reported in Australia (French et al., 1984 ) . Maize grain ranges from 14 ? 20 kg ha mm - 1 ; maize forage biomass ranges between 28 - 34 kg DM ha mm- 1 ; rice ranges between 7.1 ? 8.1 kgDM ha mm - 1 (Zhang et al., 2005); grain legumes range between 2.5 - 15.9 kg ha mm - 1 and 11.7 - 38.7 kgDM ha mm - 1 for forage biomass (Siddique et al., 2001) ; and potato tuber ranges from 62 - 116 kg ha mm- 1 (FAO, 2009) . The CWP of pasture is benchmarked at 20 kgDM/ha/mm, with a range from 0.7 to 21 kgDM/ha/mm in New Zealand (Martin et al., 2006). The CWP review suggests that grain legumes have low CWP and potato a C3 plant, has the highest CWP amongst some of the world?s major crops. 2.2.2.2 C rop- water production function and irrigation water use efficiency Irrigation management is rational when all benefits (rather than yields alone) are maximised (English et al., 2003) . Total benefits are measured by the increased net yield and income per irrigation increase, the relief of environmental influence and produc tion costs. Studies have shown that optimisation of total benefits depends on the crop yield relationship with water inputs: that is, crop - water production function (Geerts et al., 2009) . Crop water production function works as a tool for assessing profita ble consequences and for making decisions on strategies for water management, when water is scarce (Igbadun et al., 2007) . The relationship of applied water to yield (water production function) is curvilinear (Fig. 2.1) , due to several water losses through run- off, surface evaporation, deep percolation and excessive water use. Figure 2.1 deduces that water supply from rainfall in section A are insufficient for maximum yield, as a result water productivity is low and curve shape is more like convex or quadr atic. There is need to increase water supply through irrigation up to Section B. Sufficient application of water in section B results in increased yield and water productivity with less yield loss or water loss, resulting into a linear curve (Geerts et al., 2009) . Further increase of water supply increase tuber yield at a decreasing rate or with small margin thereby decreasing water procuctivity as described by section C in figure 2.1. Growers do not require applying water more than ETc after section B to achieve a good ET - Y ield relationship. CHAPTER TWO Literature Review 11 Figure 2. 1 Schematic diagram illustrating water production function (A - C) and crop water production function (A - B) concept for potato. The ET- yield relationship (crop water production function) is reported to be linear because increase of crop water consumption increases tuber yield at an increasing rate up to optimum production (English et al., 2003; Kasyap et al., 2002). However, Ferreira et al. (2007) has reported both relationships to be linear in potato, where the yield response to applied water (52 - 91 kg ha mm - 1 ) and ET - yield (62 - 105 kg ha mm - 1 ) varied with N fertilisation. The performance of the crop water production function was a result of appropriate N and water management. It has also been reported that the selection of crop cultivars with high efficiency in water use; the use of efficient irrigation technologie; and the application of less water during crop production (deficit irrigation) , increases maximisation of total benefits from irrigation (Kirda et al., 2002). Efficient crops in water use and irrigation scheduling increase the slope of the ET - Yield thus IWUE . E fficient irrigation technologies minimise water loss to the equivalent evapotranspiration curve: that is, irrigation efficiency (IE ) . However, optimisation by water deficit, on its own, can reduce yield per unit area, despite efficient production CHAPTER TWO Literature Review 12 costs and environmental management, in addition to low water use, per yield. The combination of cultivars, novel technologies and soil fertility strategies can increase both yield per unit area and per unit of water, simultaneously. T he integration of efficient water use strategies provides primary water management strategies, which can reduce water use inefficiencies within a range of irrigation management and crop or cultivar categories by capturing leakages of water loss ? which could not be tackled through the use of only one novel method. Irrigation water use efficiency is defined as a marginal increase in total tuber yield, as a result of one extra unit of irrigation water (m 3 ) . Irrigation water use efficiency (IWUE ) is determined as the total yield difference between irrigation and the rain- fed crop, divided by the net evapotranspiration for irrigated crops, according to Howell ( 2001) as presented in Equation 2. 1: where Y i is the yield and ET i is the ET for irrigation level i, Y d is the yield and ET d is the ET for equivalent w ater in the rain- fed plot: and I i is the amount of irrigation applied for irrigation level i. Irrigation WUE, as a tool, evaluates the relative advantages of irrigation management to a rain- fed production system or crop cultivars. 2.2.2.3 Economic water productivity Hoekstra et al. (2009) indicated that efficient water use is rarely achieved in agriculture, because water prices are lower than their real economic value. In addition, water is not privately owned and there has been a failure to cost the externalities that water users cause to the environment. In practice, assessment of the economic impact of a water footprint is difficult. Therefore, the cash per volume of water used and economic loss of not using the most competent crop cultivar or technology, for water saving, is assessed by economic water productivity (Molden et al., 2001) and economic water loss per unit of water used (EW L) , respectively . E conomic water productivity and EWL are used as partial economic analysis of efficient water use strategies in Agriculture (Hoekstra et al., 2009). Economic water productivity (NZ$/m 3 ) is estimated as the overall present value of each crop?s marketable produce (NZ$ ), divided by the actual volume of water (m 3 ) consumed IWUE = ????????? ???? ???? ????????? ????????????? Equation 2.1 CHAPTER TWO Literature Review 13 by the plant (Molden et al., 2001). The economic loss, per water unit used in producing an economic yield, is determined by multiplying the product price by the difference between the potential water productivity and the actual water productivity of that particular product (Chapagain et al., 2005; Hoekstra et al., 2009). Hoekstra et al. (2009) assumed that potential WUE and actual WUE have the same cost and water saved can be re- allocated to produce more of the same crop variety: and the price of the product is not variable. However, this thesis uses economic water productivity or cash per volume of water used for production (Aldaya et al., 2008) only because it was difficult to identify potential CWP for all studied heritage crop cultivars. 2.2.3 Water footprint or virtual water content (m3 tonne-1) of growing crops Virtual water content, as defined by Hoekstra (20 03), is t he amount of water required to produce the product at a place and time, where or when the product is needed. T he water footprint refers to the cumulative volume of water needed for growing a unit of crop biomass ( m3 tonne- 1 ) (Hoekstra et al., 200 7; Hoekstra et al., 2002 ) . These two terms are sometimes used interchangeably and they are both important when assessing how much water will be saved, when producing a particular crop instead of producing an alternative crop. B oth terms indicate the production method which has the least burden on the environment (Hoekstra et al., 20 03). Virtual wate r content (VWC) is more concerned with food production and trade at the point of consumption (Renault et al., 2002) . W ater footprint (WF) is more associated with food production and environment at the point of production. Values of water footprints ( m3 tonne- 1 ) are influenced by the same factors that affect CWP. However, water footprint is different from CWP because it is subdivided into three components: consumption of rainwater (green water footprint); surface or groundwater (blue water footprint); and volume of water required to absorb pollution (grey water footprint), which includes both direct and indirect water use (Hoekstra et al., 2009). The sum of these components is the total water footprint, whereas the sum of the green and blue water footprint is the consumptive water footprint. The CWP determination hardly includes the grey water footprint, or the separate components of green and blue water. It only includes consumptive water (blue and green water) as a single component. The consumptive water footprint is inversely related to CWP. CHAPTER TWO Literature Review 14 Globally, the consumptive water footprint for irrigated crops is smaller than that for rain- fed crops, due to yield increase as a result of irrigation (Mekonnen et al., 2010a) . It has also been found by Mekonnen et a l. (2010b) that a complete rain- fed agriculture is comprised of 91% green and 9% grey water, whilst supplementary irrigated crops have 48% green, 40% blue and 12% grey water, and the consumptive water footprint is comprised of 78% green and 12% blue water. 2.2.3.1 Typical water footprint and virtual water content for a range of crop categories The value of a typical water footprint and virtual water content for crops depends on the harvestable product and whether it is related to the edible part, oil extraction or total biomass. Recent studies have shown that crops grown for food have a lower water footprint than crops specifically grown for energy and for oilseeds (Gerbens - Leenesa et al., 2009a). Gerbens - Leenesa et al. (2009b) found that the average water footprint of growing crops for biomass production, in four countries, was lowest in potato (120 m 3 tonne- 1 ) and sugar beet (163 m 3 tonne- 1 ), whereas cotton (3494 m 3 tonne- 1 ) and soybean (2265 m3 tonne- 1 ) were reported to have the highest wat er footprint. The water footprint of growing primary crops was found to increase for sugar crops (200 m 3 tonne- 1 ), vegetable (300 m3 tonne- 1 ), tuber crops (400 m3 tonne- 1 ), fruits (100 0 m 3 tonne- 1 ), cereals (1600 m 3 tonne- 1 ), oilseed crops (2400 m 3 tonne- 1 ) and pulses (4000 m 3 tonne- 1 ), according to Mekonnen et al. (2010b). There is spatial variation in the water footprint for producing the same crop, as reported by various scientists from different parts of the world. On average, sugarcane and potato have a small water footprint, whereas soybean requires more water to produce one tonne (Hoekstra et al., 2003 ). The water footprint (WF) of growing potato ranges from 160 ? 250 m3 tonne- 1 . ( Hoekstra et al., 2003; Zimmer et al., 2003; Kumar et al., 2007); WF of wheat ranges from 1150 ? 2000 m3 tonne- 1 (Hoekstra et al., 2003; Zimmer et al., 2003;Chapagain et al., 2005); WF of rice ranges from 1400 - 3600 m3 tonne- 1 (Hoekstra et al., 2003; Zimmer et al., 2003; Chapagain et al., 2006); WF of maize ranges from 450 - 1900 m3 tonne- 1 ; soyabean ranges from 2300 ? 4000 m3 tonne- 1 (Hoekstra et al., 2003; Zimmer et al., 200 3; K umar et al., 2007) ; WF of pumpkin ranges from 238 - 240 m3 tonne- 1 ; Kumar et al., 2007); and WF of sugarcane ranges from 150 - 200 m3 tonne- 1 (Kumar et al., 2007; Mekonnen et al., 2010a ). The review shows that WF is lowest in CHAPTER TWO Literature Review 15 potato and sugar cane and highest in soyabean and cotton. However, the wide variation in WF suggests a need for further measurements, in order to enhance general WUE in areas with a spatially high water footprint. 2.2.4 Nitrogen use efficiency Nitrogen use efficiency (NUE) for potatoes is defined as the ratio of tuber yield to the amount of N applied for its production (Battilani et al., 2004; Darwish et al., 2006) . It has been documented that NUE increases with restricted N application, whilst maximum N application reduces NUE in potato (Zebarth et al., 2008; Darwish et al., 2006) . Irrigation is said to enhance NUE in potato compared to water stress, whilst an N increase also increases WUE, because WUE and NUE are positively and linearly related (Battilani et al., 2004 ). However, improvement of NUE is also challenged by the way agronomic and physiological features are integrated, in addition to genetic approache s to achieving efficiency in nitrogen use (Hirel et al., 2007) . 2.3 Soil?Plant?Atmospheric Continuum (SPAC) and Physiological WUE 2.3.1 Plant water uptake and soil or root system Agriculture, as a human activity, disturbs and modifies the nature of the plant ecosystem, in order to meet man?s interest. The s ustainability of such plant ecosystems is only possible with proper management of soil, water and nutrient balances, in response to the atmosphere and its climate components, within a modified system, (Raes et al., 2009) . Naturally, the plant - water system within the ecosystem has water moving from the soil ? root ? stem ? leaf ? atmosphere, thus forming a continuous column of water called the soil- plant- atmospheric continuum (SPAC), with stomatal and non- stomatal controlling mechanisms (Phillip, 1966; Rose, 1996) . Subsequently, the physiology of WUE ( within the SPAC ) primarily depends on t he leaf stomata, which responds to the atmosphere and soil environment, as a main regulation point for transpiration in plants (Raes et al., 2009) . CHAPTER TWO Literature Review 16 2.3.1.1 Stomata conductance response to atmosphere and soil environment Stomata conductance (g s ) is an essential physiological characteristic associated with crop production. Stomata conductance (g s ) mainly regulates photosynthesis (A n) and transpiration (T), depending on the environmental factors (Wright et al., 2008) . High leaf temperature raises atmospheric vapour pressure deficits, which then induces stomatal conductance (Sinclair et al., 1984) . The implication of a high water vapour gradient results in leaf water deficits, thereby, declining An and T rate (Bunce, 2003 ) . It has been asserted that optimal stomatal opening for An is induced by high photosynthetically active radiation ( PAR ) and optimal soil moisture: whereas its closure is induced by high leaf water potential approached after maximum leaf transpiration and water deficits (Vos et al., 1987) . Water deficits in the soil and atmosphere always affect the SPAC, thus causing the leaf stomata to close and thereby reducing carbon dioxide entry for photosynthesis ( Weatherley, 1976). The stomatal closure is the pri mary constraint to An and T caused by mild to moderate water stress. This is initially signified by gs, and internal carbon concentration (Ci) declines with mild or moderate water stress. The progressive build - up in water stress results in secondary restrictions to An in C3 and C4 plants, caused by an integration of stomatal and mesophyll conductance (Flexas et al., 2002; Ripley et al., 2010) and biochemical mechanisms (Galm?s et al., 2007) . The mesophyllic limitation is envisioned by low stomatal aperture, without affecting Ci (Schapendonk et al., 1989) . The literature confirms potato genetic differences in stomata resistances, leaf area index , canopy expansion and photosynthetic WUE, when the plant is exposed to different atmospheric water demands and soil moisture ( Jefferies et al., 1993b ). The gaseous exchange in potato are reported to greatly differ with leaf age ( Vos et al., 1987; Ghosh, et al., 2000) , genotypes (Tekalign et al., 2005), irrigation (Ahmadi et al., 2010) , nitrogen ( Ghosh et al., 2000; Olesinski et al., 1989) , and climate factors. Severe water stress is accelerated by high leaf vapour pressure deficit (VPD) (Bunce, 200 3). Galmes et al. (2007) investigated constraints to photosynthesis in C3 plants under water deficit and discovered that stomatal and mesophyll conductance were the major limiting factors, whereas the biochemical effect was insignificant. His findings concur with CHAPTER TWO Literature Review 17 Flexas et al. ( 2002) who reiterated that restrictions to photosynthesis become rigorous with water stress increase. On the other hand, the consequence of stomatal or mesophyllic restrictions to photosynthesis vary: stomata closure by water stress is said to improve photosynthetic WUE, by reducing transpiration more than photosynthesis, whilst mesophyllic activity does not affect photosynthetic WUE in potato, since both transpiration and net photosynthesis declines ( Schapendonk et al., 1989). Photosynthesis resumption, after severe water stress, depends on the resilience of each genotype ( Galmes et al., 2007) . Optimal water and N increases An, T and photosynthetic WUE in potato ( G hosh et al., 2000). In another study, Ahmadi et al. (2010) found similar high potato An between full irrigation (FI) and partial root - zone drying (PRD), but low A n with deficit irrigation (DI), as also observed by Liu et al. ( 2006b). These results demonstrate that A n is greatly restricted by severe water stress in potato, as once reported by Vos et al. (1989a b). The photosynthetic WUE of PRD was found to be greater than DI and FI, thus confirming the sparing water use in PRD. In contrast, Liu et al. (2006b) found photosynthetic WUE and WUE to be similar between FI and PRD, but lower in DI, thus contradicting the statement that PRD has high photosynthetic WUE, compared to FI (Ahmadi et al., 2010; Kang et al., 2004) . Liu et al . (2006a ) reported a reduction in potato dry matter production and photosynthetic WUE with deficit irrigation, thus confirming that water stress decreases potato production, as observed by Wolfe et al. (1983) . The review confirms that water stress restricts WUE on biomass and photosynthetic basis in potato and in other C3 plants and that water stress effects may vary with cultivars and different soil types. 2.3.1.2 Soil media The soil conducts and contains water and nutrients, depending on its hydraulic characteristics. Usually, plants close their stomata when the amount of water in the soil media is nearly at wilting point (1500 kPa) , and they open the stomata when the amount of water is readily available at field capacity (10 - 33 kPa) (Ahuja et al., 1990; Scotter, 1977; Sumanasena, 2003) . The field capacity in New Zealand is estimated as being from 4.9 to 10 kPa (Sumanasena, 2003) . Globally, the optimum soil water tension, for potato, is betwee n 5 kPa and 33 kPa (Shock et al., 2007) . Nevertheless, the maximum CHAPTER TWO Literature Review 18 water holding capacity for soil media depends on its hydraulic conductivity, plant root zone depth for the crop cultivars being cultivated and the amount of water in the supply. A well- developed root- zone enhances the roots to respond to the atmospheric demand: and it regulates the plant shoots, during a crisis of water stress, so that the stomata can keep the water in balance within the plant (Hoogland et al., 1981) . Nevertheless, potato roots are very shallow and less dense for tapping deep soil water (Hoogland et al., 1981 ; Shock et al., 2007 ) . Consequently, a water deficit instantly lowers the physiological WUE in potato, as discussed above . Similar to any plant, potato is well coordinated ( through roots, shoots and stomata ) to soil water balance situations in the soil and atmospheric demand called potential evapotranspiration ( ETp) . 2.3.2 Evapotranspiration and irrigation requirements The available soil water supports plant transpiration and root water uptake, in order to meet potential evapotranspiration demand (Monteith et al., 1986) . Potential evapotranspiration ( ETp ) refers to the volume of water that a crop could have consumed, if the water resource was adequate, whilst net water use for a crop is referred to as the actual crop evapotranspiration (ETc) ( Pidwirny, 2006). In reality, potential crop water use is equivalent to crop evapotranspiration: that is, the volume of water to be replaced, in order to meet potential potato yields (Allen et al., 1998). Evapotranspiration, within the SPAC, is influenced by aerodynamic res istance, stomatal resistance, canopy resistance, radiation, temperature, and relative humidity (Allen et al., 1998) . Evapotranspiration demand is reported to be equal to the plant root ability for water uptake, when it is equal to water uptake, translocation and transportation: but when evapotranspiration demand is above the root ability, the crop closes its stomata (Ziemer, 1979) . The interaction between atmospheric demands, the water potential of the leaf , the resistance of water movement in the plant and the soil water potential, depends on the soil moisture ( Phillip, 1966). The difference between the evapotranspiration demand (crop water requirement) and the water supply (rainfall plus capillary rise) to the potato roots is what is referred as the ?net irrigation requirement for meeting potato evapotranspiration demand? (FAO, 1997b) CHAPTER TWO Literature Review 19 Potato evapotranspiration differs with genotypes, location and season, however, Allen et al. (1998) documented that the seasonal potato ET c ranges from 500 - 700 mm for maximum yield. The seasonal potato ET c variation widens with the season, a humid winter recorded 250 - 31 2 mm, whilst a summer season was recorded at 380 - 584 mm ( Bowen , 2003) . Wright and Stark (1990 ) reported a maximum potato ET c of 450 - 700 mm in the U SA. In Turkey, potato ET c was reported to vary between 226 - 473 mm and 166 - 391 mm under surface and sub- surface drip irrigation (Onder et al. 2005) , whilst Erdem et al. (2006) reported ET c of 673 mm and 524 mm for furrow and drip irrigation within Turkey. Kasyap et al. (2003) determined potato ET c ranging between 164 - 280 mm in India, using 30 - 75% depletion irrigation scheduling, whilst Panigrahi et al. (2001) reported ET c of 200 - 320 mm within India. Yuan et al. (2003 ) determined potato ET c of 400 mm under drip irrigation in Japan. Potato e vapotranspiration variations indicate that each location and genotype requires its own recommendation of ET c , otherwise maximum yields may not be realised. Crop evapotranspiration for New Zealand, especially in the eastern region, is expected to increase with climate variability (Kevin, 20 01) . The drought affected areas, or seasons, are expected to have a higher evaporative demand than the normal seasons (Mullan et al., 2005) . The summer drought is expected to increase the VPD and reduce the soil water content below field capacity. Summer drought will affect the SPAC of all crops in New Zealand (Kevin, 2001) . Drought will increase water deficits by 50 - 250 mm potential evapotranspiration (ET p), with a maximum annual ET p of 300 - 500 mm, in the driest regions of New Zealand (Mullan et al., 2005) . The change in ETp is expected to increase irrigation by 55% for each decade ( Mullan et al., 2005; New Zealand govt., 2000) . Broadly speaking, climate variability in New Zealand will result in more economic water scarcity than physical water scarcity (IMW I, 2002 ) . The rise in pumping costs will reduce the profitability of irrigated crops, resulting into economic water scarcity. Clothier et al. (2010) expressed concern that New Zealand is one of the countries that is showing a very high increase in total agricultural water use and irrigated areas, over the past decade. However, Australia has managed to increase its irrigated areas, despite a decrease in agricultural water use, due to efficient water use. The performance of Australia suggests that there are opportunities to reduce agricultural water use in New CHAPTER TWO Literature Review 20 Zealand, by following novel technologies (Clothier et al., 2010 ) . An understanding of alternative crops, crop genotypes and agronomic practices, which use water sparingly, is another priority for the adjust ment to high evaporative demand, besides novel irrigation technologies. Taewa and other heritage crops are some of alternative crops that can contribute to sparing water use in New Zealand. 2.4 Taewa species and production trend in New Zealand Taewa ( Solanum tuberosum) is a collective name for all potatoes cultivated by Maori people in New Zealand since the 18 th century (Rosk ruge, 1999) . Taewa originated from South America in th e region of Peru and Chile (Roskruge et al., 2010). Maori people redomesticated it in New Zealand , either from early European explorer or trading vessels from South America. Taewa cultivars were then developed through potato seedling selection and selection of true potato seed from potato berry (Harris et al., 1999; Harris, 2001). Taewa cultivars can be grouped into dark skin, multiple coloured, red skin, creamy, brown or light coloured skin and others with pink or w hite skin (Harris et al., 1999 ) . The commonest Taewa cultivars in New Zealand include: Hukaroro, Pawhero, Karuparera, Ngauteuteu, Raupi, Tutaekuri, Moe Moe and Wherowhero (Plate 2.1; Harris, 2001). Tutaekuri belong to Solanum tuberosum s ubsp. andigena Juz & Buk (Peruvian/Andean) while the other Taewa cultivars are Solanum tuberosum subsp. tuberosum L ( Chilean) (Rosk ruge et al., 2010). Harris et al. ( 1999) out lined East Coast ? East Bay of Plenty region and the Hawkes B ay, Wairarapa, Northland and Rangitikei as the main production area of Taewa in New Zealand in the early 19 th Century. Taewa production among the Maori in these regions had enforced social- economic attributes on geneology and creation, kinship and family relationship, spiritua lity, hospitality and kindness, customs and habits, and economic survival (Ros kruge, 1999) . However, by 1998, Roskruge could not find more scientific information and production trends related to Taewa production (Rosk ruge, 1999) . The main reason was that Taewa production among Maori did not receive enough support from New Zealand Government on disease and pest control compared to commercial farmers. M ost of the Taewa cultivars were susceptible to leaf blight. Consequently, Taewa production was the most affected during the 1905 ? 1906 leaf blight epidemic (Harris et al., 1999) . CHAPTER TWO Literature Review 21 Taewa production trends are also scanty because most scientific research on Taewa is primarily social in nature, except the study by Roskruge, (1999), Hayward (2002) and Harris (2001) . Taewa research since 1999 includes: (1 ) Taewa Maori : their management, social importance and commercial viability by Roskruge, (1 999) ; (2) Nga Riwai Maori- Maori potatoes on an Ethnobotany basis by Harris (2001) ; (3 ) E ffect of nitrogen and plant density on the growth and development of Taewa by Hayward (2002 ) ; (4 ) The contribution of Taewa (Maori potato) production to Maori sustainable development by McFarlane (2007) ; (5 ) The expansion of sustainability through New Economic Space: M?ori potatoes and cultural resilience by Lambert (2008) ; and (6) The lifecycle and epidemiology of Bactericera cockerelli on three traditional Maori food sources by Puketapu (2010) . These studies have established that Taewa is equally important as modern potato across New Z ealand and Australia. Roskruge et al. (2010) indicated that the tough times and harsh environment that Taewa went through in the 19 th century, made Taewa to be hardy and disease resistant. However, management and crop physiology characteristics are the setbacks impeding Taewa production ( Roskruge, 1999; Roskruge et al., 2010) . Taewa yield is physiologically handcapped by its tuber number and tuber size characteristics. Taewa cultivars of Kowiriwiri, Tutaekuri were reported to have late establishment and low tuber yield compared to commercial cultivars of Red K ing Edward and Ilam Hardy ( Ros kruge , 1999) . Ilam hardy yielded 1.8 kg / plant as compared to Tutaekuri with 0.92 kg/plant. A followup study by Roskruge (1999) on t en Taewa cultivars, tuber yield ranged from 1.04 kg/plant to 1.8 kg/plant. Moe Moe had the highest tuber yield among Taewa but lower than Red K ing Edward. Harris (2001) also reported that Rua , a commercial cultivar yielded 1.52 kg /plant compared to T aewa with 0.74 kg/plant. Hayward (2002) also studied Kowiriwiri, Tutaekuri, Matariki and Moe Moe in comparison with modern cultivar, Red King Edward. Tuber yields were highest in Moe Moe (4.5kg/plant) and lowest in Matariki (2.4kg/plant). The commercial cultivar, Red King Edward was outyielded by Mo e Moe suggesting possibility of higher potential yield in some Taewa cultivars than commercial cultivars. CHAPTER TWO Literature Review 22 Plate 2. 1 Varieities of traditional Maori potatoes (Taewa) in New Zealand sourced from Roskruge, N, Massey University, 2012 The high number of tubers of small size in Taewa and traditional management methods practiced by Maori were alleged to be the main cause of lower tuber yields in Taewa (Ro skruge, 1999; Ro skruge et al., 2010). On the other hand, Taewa has great busine ss potential because of its easiness to grow and potential commercial attributes due to the people?s growing interest in traditional crops at national and internation market. Methods for seed selection and disease control applied by Taewa growers were repo rted to be unscientific (Walker, 1997). These methods and lack of irrigaton in most Taewa production system and viruses have contributed to low Taewa tuber yields ( Ro skruge, 1999). Strategies for maximising crop water and nitrogen productivity or breeding for high productivity that was employed in modern potato cultivars was not consistent with heritage potato, Taewa. CHAPTER TWO Literature Review 23 2.5 Strategies and constraints for maximising crop water and nitrogen productivity in modern production systems 2.5.1 Opportunities for maximising WUE in agriculture Water use efficiency in agriculture is maximised through innovative irrigation and biological water- saving technologies : deficit irrigation (English et al., 1996) , partial root zone drying (Wang et al., 2009b) , drip irrigation, the use of crops with high water to biomass conversion ability (McLaughlin, 1985; Steyn et al., 1998) , agronomic measures, including irrigation scheduling (varied irrigation) (Hedley et al., 2009a b) , mulching, fertilisation and co nservation farming, in relation to crop cultivar selection (Zhang et al., 2005) . The emphasis for this review is on how cultivars and agronomic measures of irrigation and N management enhance WUE in agriculture. Morison et al. (2007) established that crops which transpire and fix more carbon per unit of water ? and those that allocate more assimilates toward the harvestable yield ? provide more opportunities for maximising WUE, than others within the same management and environment . Furthermore, non- water input (fertilisation and cultivar selection) and irrigation factors integrate well together, in order to capture optimum water for transpiration (Morison et al., 2007) and strengthen the sink (Viets, 1962) . These opportunities suggest a balance of input factors in agriculture, or otherwise, the deficit in one factor can reduce leaf expansion ( Jefferies et al., 1993a ), resource use and transpiration (Imma Farre et al., 2006; Tanner et al., 1983 ) . This observation supports the finding that WUE of potato in nutrient deficient soil is limited by transpiration, from reduced LAI and reduced allocation of biological assimilates into the sink (Jefferies et al., 1993b) . Transpiration and LAI are related . An increase in the canopy increases crop water use, whilst decreasing evaporation (Ritchie, 1983) . Evapot ranspiration only relies on soil surface prior to the development of a full canopy but (as the canopy grows) evaporation declines due to soil cover. One role of nitrogen ( N ) , in this process, is the facilitation of fast growing roots and canopy establishment, in order to enhance the WUE, which depends on soil water storage. WUE which is met by decreasing evaporation or runoff whilst increasing soil water storage, increases total production per unit of water available for agricultural use. However, it does not increase biomass production per unit CHAPTER TWO Literature Review 24 of water evaporated from the same area (Tanner et al., 1983) . With the limits of course, the greater the transpiration, the greater the total photosynthesis, therefore the greater the plant production. Water use efficiency, per unit of water available and evaporated from the same area, improves with high water productive genotypes and agronomic practices, which reduce evaporation (Howell, 2001; Sinclair et al., 1984) . This supports a deliberate change, from low water productive crops, to high water productive crops (Hoekstra et al., 2007; McLaughlin, 1985) . The optimal irrigation and fertilisation reported in rice (Zhang et al., 2005) and potato are also the best means for increased water productivity (Darwish et al., 2006) . Furthermore, some indigenous and wild potato crops or cultivars ( Zebarth et al., 2004, 2008), wild oilseeds, jojoba ( Simmondsia chinensis Schneider), guayule ( Parthenium argentatum Gray) are also reported to reduce their water and nitrogen use, without a decline in their yields, under both rain- fed and irrigated conditions ( McLaughlin, 1985) . The variation in allocation and rate of assimilation offered by various heritage or old crop cultivars and agronomical strategies can provide alternatives for crop diversification, in times of water scarcity (Bessembinder et al., 2005) . The substantial opportunities for maximising resource use in agriculture focus on a combination of strategies, which use the concept of ?Water Use Efficiency (Barker et al., 2003) . In conclusion, the high yield and WUE apparent in most modern crop production systems relies on a combination of factors, including appropriate site selection, pest and disease control and optimum ma nagement of inputs, rather than just simple genetic improvement (Richards et al., 2002 ). 2.5.2 Water and nitrogen management in modern potato production Potato water requirements range from 400 - 800 mm (Ekanayake, 1989; Allen et al., 1998; FAO, 2002), whilst N requirement is 235 Kg N ha - 1 , within a 120 - 150 days growing period (Westerman, 2005). In New Zealand, Craighead et al. ( 2003) recommended 200 - 250 kg N ha - 1 for main crop potatoes and 300 kg N ha - 1 , where the season is very long. W inter potatoes were recommended at 160 - 240 kg N ha - 1 for maximum yield and minimum N leaching. The N estimate for New Zealand has been CHAPTER TWO Literature Review 25 confirmed by Martin et al. (2001), when they found no tuber yield increase with N over 242 kg N ha - 1 at Pukehoke. However, most growers in New Zealand still use 400 kg N ha- 1 . I n Australia, N rates of 80 - 120 kg N ha - 1 were recommended as sufficient rates for obtaining 80 - 350g tuber sizes, for crisp production (Dahlenburg et al., 1990). Sparrow et al. (2003) investigated Russet Burbank response to basal dressing up to 250 kgN ha - 1 and top dressing up to 100 kg N ha - 1 in Tasmania and found that top dressing did not enhance tuber yield, compared to basal rates. In another Australian study, Brown et al. (2008) found no difference between N side dressings (0, 125, 250, 500 kg N ha - 1 ) on tuber yield. They also found no significant N leaching with N up to 300 kg N ha- 1 , because the potato removed 250 kg N ha - 1 . Alva et al. (2009) recommended 112 + 112 kgN ha - 1 for basal and top dressing in USA, respectively. The side dressing was recommended to be applied five times from four weeks from planting, at two week intervals, based on his N and reduced tillage research using a centre pivot irrigator (Alva et al., 2009) . Nitrogen recommendations are variable between and within countries, due to soil status and objectives. Nitrogen is needed for growth during the first half of the growing season whilst N applied later is stored in the tuber (Belanger et al., 2002). Darwish et al. ( 2006) also found that a lower N rate (125 kg N ha - 1 ) results in a satisfactory N uptake, compared to a high application (500 kg N ha - 1 ). Haverkort (2003) found that 200 kg N ha - 1 was optimal: and any excess above that amount would decreas e the tuber yields. This finding supports other findings which show a tuber yield decline with high rates in N application (Vos et al., 1997) and water deficit ( Martin et al. 1992) . Irrigation was recommended on a weekly basis during dry periods by Marti n et al. (1992), to meet over 440 mm water requirement in New Zealand. Martin et al. (1992) also reported tuber yield reduction in potato with water deficit, as reported by Bowen (2003), Darwish et al. (2 006), Kang et al. (2004) and Shock et al. (2007). S hock et al. (2007) recommended that growers needed to irrigate the correct amount of water at the correct time and also monitor soil moisture and agro- meteorological data, for precise potato irrigation. Maximum tuber yield and minimum land pollution can only be achieved when water use is near potential crop evapotranspiration. It has been reported CHAPTER TWO Literature Review 26 that correct irrigation scheduling, using estimated evapotranspiration and soil water tension, optimises potato water use for maximum tuber yield (Shock et al., 2007). Water deficits of 65 - 70% of soil available and water and soil water potential of - 25 kPa reduce marketable tuber yields by 31 - 68%, due to poor tuber quality and poor tuber weight (Shock et al., 2007; Darwish et al., 2006) . Battilani et al. ( 2008) also reported that optimal moisture without N fertilisation ? and N fertilisation with water deficit or excessive water ? both decrease potato growth and tuber yields. Henceforth, the benefit of N on yield depends on the correct time and amount of wa ter and N application (Haverkort, 2007). Soil moisture and N availability also affects the choice of potato cultivars, because there are significant genotypic differences in response to water use (Laurence et al., 1985; Steyn et al., 1998) . Sinclair et al. (1984) showed that some potato cultivars use water more efficiently, and some tolerate drought better than others (Steyn et al.,1998) . In contrast, other findings report no significant variations between potato cultivars, in response to water and N supply (Dalla Costa et al., 1997; Belanger et al., 2002) . In New Zealand, significant differences in yields between modern cultivars and Taewa, have also been reported (Harris et al., 1999) . However, Taewa has not been rated w ith modern cultivars on different water and N regimes. Hayward (2002) attempted to assess Taewa response to N and population density, but the study did not reach a clear conclusion. 2.5.2.1 Dry matter partitioning and tuber yield in response to irrigation and nitrogen Growth and dry matter partitioning Potato growth and partitioning of dry matter (DM) to leaves, stems, roots and tubers, vary with potato genotypes, water, N and growth stage (Geremew et al., 2007) . Partitioning to leaves, stems and tuber, within 50 - 60 days from planting, was reported to be similar (but varied over time) between newly released and old commercial cultivars in South Africa (Geremew et al., 200 7) . Tuber formation between cultivars was found to be in three categories: early tuber set with rapid harvest index (HI) increase; early tuber set with slow HI increase; and late tuber set with gradual HI increase (Geremew et al., 2007) . Geremew et al. (2007) also observed a reduction in CHAPTER TWO Literature Review 27 partitioning to tubers and tuber yield in cultivars with the highest canopy, LAI and DM, compared to cultivars with the least LAI, canopy and DM. Errebhi et al. (1999) reported that commercial potato cultivars partitioned more to tubers, whereas wild potato allocated more to shoots: and their hybrids were intermediate. Commercial cultivars partitioned 1% (roots), 15% (shoots), 0% (fruits), 84% (tubers), whereas wild cultivars allocated 18% (roots), 52 % (shoots), 23% (fruits) and 7% (tubers): and their hybrids allocated 9% (roots), 39% (shoots), 14 % (fruits) and 14% (tubers). Traditional barley cultivars (Abeledo et al., 2011) and old wheat cultivars (Siddique et al., 1990a ) were also reported to optimise allocation of assimilates to non- harvestable products, compared to new modern cultivars. The review shows genotypic variation in dry matter partitioning and also that most traditional or old cultivars increase LAI and canopy development at the expense of harvestable products. Tuber yield and WUE for modern potato The average tuber yields for modern potato cultivars ( e.g Moonlight, Dawn, Kamai, Karaka, White Delight, Driver and Pacific), during the time of their release, ranged from 38 to 55.4 t ha - 1 in New Zealand (Anderson et al., 2004; Genet et al., 1997; Genet et al., 2001) . Early studies by Craighead et al. (2003) reported a tuber yield increase from 50.3 to 52.4 t ha - 1 in Ilam Hard y; 72.2 to 76 in Fiana; 50.5 to 50.6 in Kennebec; and 51.9 to 79.3 in Russet Burbank with N increase, from 150 to 300 kg N ha - 1 . The other study on Russet Burbank yield ranged from 55.2 to 73.3 t ha - 1 , in New Zealand. The highest tuber yield increase with N application was found in well watered and the lowest increase in drought plots (Martin et al., 1992) . The yields for modern potato are double the current mean total and marketable tuber yields attained by Taewa growers, which range from 15 - 20 t ha - 1 and 10 - 15 t ha - 1 , respectively (Roskruge, pers. comm., 2011). The early studies on Taewa and modern potato cultivars presented in section 2.4 also proved that modern potat o yield are more than twice the yield of Taewa ( Roskruge, 1999; Harris et al., 2001). The gap on average tuber yield and WUE between the world (with an average of 15.9 t ha - 1 ) and those reported across world experiments ( with an average of 30 - 60 t ha- 1 ) is also reported to be very wide (Bowen, 2003; Sale, 1973) . Such yield disparities are accelerated by climatic conditions, genotypes, soil and water management factors (Shock et al., 2007) . CHAPTER TWO Literature Review 28 The Asia and Pacific region also experien ces an average potato yield gap. The average tuber yield is 15.7 t ha - 1 , with the highest average yields ranging from 45.3 - 52 t ha - 1 in New Zealand, and the lowest average tuber yields of 2.5 t ha - 1 in Timor- Leste (Pandey, 2008) . Worldwide experiments have confirmed that pota to yields and WUE vary with location and management (B?langer et al., 2002; Darwish et al., 2006; Ferreira et al., 2007; Starr et al., 2007) . The average potato yields in New Zealand are also higher than those reported in many other countries. Extraordinary tuber yields of 88 - 89 t ha - 1 were reported by Kunkel, as quoted by Sale (1973) . Brown et al. (20 08) also reported yields of 75 - 80 t ha - 1 in Australia. In New Zealand, Craighead et al. (1999) and Sinton (2007) reported potential yields of 80 t ha - 1 . H owever, farmers only realise an average of 60 t ha - 1, (40 - 80 t ha - 1 in their main crop and 15 - 50 t ha - 1 in the early crop). Th e failure to reach the potential tuber yield is caused by water and N stress (Sinton, 2007) . E fficient management of water, N and genotypes, can reduce the tuber yield gap experienced in New Zealand and other parts of the world. Sprinkler irrigation increase s tuber yield of Ilam Hardy four - fold in New Zealand (F oot, 1974) . Drip irrigation and fertigation also increase s tuber yields and WUE of potato, compared to furrow irrigation (Janat, 2001; Starr et al., 2007) . In Turkey, Erdem et al. (2006) reported a WUE of 4.7 to 6.63 kg m - 3 for furrow irrigation and 5.19 ? 9.47 kg m - 3 for drip irrigation, whilst Martin et al. (1992) reported a high WUE of 12.8 to 16.7 kg m- 3 , under drip irrigation in New Zealand. A study on irrigation of Agria potato cultivar in Iran, by Bahramloo et al. (2009), reported tuber yield and WUE decrease from 28.6 to 24.6 t ha - 1 and 2.4 to 1.8 kg m - 3 , respectively. The use of more water than 664 mm in full irrigation (1340 mm) was suspected to have declined the tuber yield and WUE . Subsequently, p artial irrigation had a high IWUE of 13.2 kg m - 3 (Bahramloo et al., 2009) . The majority of the results on efficient water use indicators in other countries may differ from New Zealand, due to weather differences. Nevertheless, this review indicates that potato has higher WUE and tuber yield potential than many crops and that there are genotypic variations in WUE (FAO, 2008; Kang et al., 2004; Trebejo et al., 1990) . Despite improvement in potato CHAPTER TWO Literature Review 29 yields, the gap between the actual yield and the potential yield is still very wide. The gap shows that potato potential yield in some cultivars is not yet fully exploited. 2.5.2.2 Tuber quality response to irrigation and nitrogen. Potato tuber quality is assessed based on tuber dry matter ( DM) , specific gravity (SG), reduced sugar content, nutritional value and external tuber shape and size (Westermann et al., 1994) . Irrigation and N reduces SG and DM. The N effect on SG and DM is significantly higher with irrigation, compared to water stress (Lawrence et al., 1985; Dahlenburg et al., 199 0). Dahlenburg et al. (1990) reported SG decrease s with N increase, from 80 ? 320 kg N ha- 1 , where as N above 150 ? 200 kg ha - 1 reduced SG . Nitrogen also increases the cases of misshapen tubers, crisps colour and hollow hearts (Sparrow et al., 2003). On the other hand, Belanger et al. (2002 ) reported a decrease of SG , with an N increase above 50 kg N ha - 1 , under irrigation. Nitrogen increases the nitrate accumulation in the tubers, thereby declining SG (Belanger et al., 2002). The effect of NO 3 - N concentration ( on stressed potato fertilised with high N ) , can be reduced by applications of water to avoid human risk (Belanger et al., 2002 quoting Carter, 1974 and Beidmond, 1992). Cultivars with small tubers had more N concentration than the large tubers, because tuber increase enhanced the starch pool (Logan, 1989 ) and protein decreased it (Belanger et al., 2002). Late maturing cultivars have also been reported as having greater SG than early maturing cultivars (Belanger et al., 2002). Similarly, sugar concentration in potato tuber increased above an acceptable range, with N increase (Dahlenburg et al., 1990). The reduction of sugar content in potato tubers according to Logan, ( 198 9) is not influenced by irrigation or N . However, other research on sweet potato ( Impomea batatus ) , by Ekanayake et al. (2004), reported that irrigation significantly reduced the levels of reduced sugars with genotype and irrigation interaction. Singh et al. (2008) compared Taewa and modern cultivars? quality characteristics and found that Taewa (Moe Moe and Tutaekuri) had higher DM and SG than modern cultivars, in New Zealand. However, Taewa quality was not assessed at varied N and irrigation, in order to identify the potential of potato quality in Taewa with different agronomical practices. CHAPTER TWO Literature Review 30 2.5.2.3 Sustainable land use implications in relation to irrigated and N fertilised potato Agricultural sustainability is described in terms of the indefinite provision of environmental, economic and social well - being benefits, with minimum negative externalities ( MacLeod et al., 2006). In the case of this review, sustainable land and water use refers to the maximisation of returns from land and water use, whilst environmental pollution is minimised. Water use efficiency is taken as a generic indicator for the implementation of sustainable crop intensification and diversification programmes and policies (Ford et al., 2009; Miskell, 2009) . Crop intensification and diversification are possible ways of adapting the agricultural system to the population growth, urbanisation and climate change challenges ( Fowler, 1999) . However, these strategies ( crop intensification and diversification) involve irrigation, heavy pestic ide and herbicide use and fertilisers, which pollute the environment (Jalali, 2005; Power et al., 1989) . Study shows that high use of N fertilizer (without any consideration of the residue remains of the previous winter greens) has increased nitrate accumulation in New Zealand, (Francis et al., 2003; Thomas et al., 2004) . Potato production (apart from dair y production) is the most inefficient land use system in terms of N loss in New Zealand (Francis et al., 2003; Sumanasena , 2003; Thomas et al., 2004) . This system registers high nitrate leaching (Francis et al., 2003; MAF, 2002) , due to high fertiliser application. Furthermore, over - irrigation flushes the nitrate- N beneath the root zone, thus causing groundwater contamination above a nitrate threshold set at 11.3 mg L - 1 in New Zealand (Ministry of Health, 1995, cited in Sumanasena, 2003) . Irrigation and N management in potato require consideration of ways to realise environmental, social and economic objectives , in addition to sustainability in agricul ture, as recommended by MacLeod et al. (2006). CHAPTER TWO Literature Review 31 2.5.3 Effects of mechanical and hormonal canopy manipulation on yield and WUE Growth regulators perform a key role in potato tuberization under the control of specific stimuli ( Chapman 1958; Kumar et al., 1973) . Major hormones reported enhancing tuberisation and growth include: cytokinin, indole - 3- acetic acid (IAA) and ethylene, gibberellic acid (GA) , abscissic acid (ABA) and auxin (Vreugdenhil et al., 1989) . Gibberellic acid hinders tuber formation by prom oting stolon elongation whilst the other hormones promote tuber formation by counteracting GA at different tuber formation stages (Vreugdenhil et al., 1989). Gibberellic acid is always artificially counteracted by foliar application of chlorocholine chloride ( Wang et al., 2009a ; 2010) . Chlorocholine chloride (CCC) is the usual name for chlormequat chloride (also known by trade name as Cycocel) . Chlorocholine chloride is one of the prominent bio- regulatory hormones that control excessive plant growth, in order to improve the root system. Chlorocholine chloride is chemically known as 2- thloroethylthrimethyl ammonium chloride with a molecular formula of C5 H 13 C 12 N . Chlorocholine chloride significantly retards above- ground growth in potato. Chlorocholine chloride also enhances the photosynthetic capacity of potato and photo- assimilates partitioning into tubers, thereby boosting tuber growth ( Wang et al., 2009a ) . Wang et al., (2009a ) reported that foliar spray of CCC to potato increased IAA whilst decreasing ABA content. The study by Wang et al., ( 2009a ) found that IAA counteracted gibberellic acid. The study by Xu et al., (1998) also found that ABA counteract ed gibberellic acid for tuberisation. Vreugdenhil et al., ( 1989) concluded that gibberellic acid is the main controller of tuber formation under the regulation of ABA, IAA and other hormones such as cytokinin and auxin which influence tuber size . However, IAA has a significant role in initiating tuber formation by retarding stolon elongation under both inducing and no- inducing environmental conditions ( Xu et al., 1998). Soil mechanical resistance (dryness, low porosity and root penetration) to plant roots stimulates Indole - 3- acetic acid (IAA) to produce ethylene (Vreugdenhil et al., 1989). The responsibility of ethylene in tuber formation in potato is short lived, but it facilitates other hormones (cytokinin, ABA) to carry on the tuber formation and development. It has been reported that some stimuli that induces this tuber formation includes grafting and short days (Kumar, 1973) and topping (Hossain et al., 1992 ), and it is hormonal in CHAPTER TWO Literature Review 32 nature (Kumar, 1973 ). Nevertheless, the effect of topping on endogenous hormones, water use and tuber yield in potato has little literature in New Zealand and worldwide . S tudies on leaf canopy manipulation have shown that the alteration of a large leaf canopy reduces water use, whilst increasing tuber yield. Water use reduction, photosynthesis and yield improvement were reported in wheat (Richards, 1983) and potato with growth hormones and topping (Rex, 1992; Wang et al., 2009 a, 2010) . The review did not identify any canopy manipulation work on potato in New Zealand. However, results from different parts of the globe show that mechanical and hormonal canopy manipulation enhances tuber yield and WUE, through dry matter redistribution and photosynthesis improvement ( Rex, 1992; Wang et al., 2009a , 2010 ) . 2.5.4 Challenges and limitations to maximisation of WUE in arable crops The options for increasing water productivity in agriculture are accompanied by several challenges and limitations (Kijne et al., 2003) , because improvement to marketable yield is required to be met with reduced transpiration and reduced outflow at farm level, whilst still increasing the economic productivity of all sources of water (Kijne et al., 2003) . I ssues of global warming and climate change are expected to instigate unexpected or unplanned water use by plants , due to expected increases in temperatures and VPD (Mullan et al., 2005; Kevin, 2001) . The main challenge is that the demand for water use is increasing, wh en attempts are being made to reduce water footprints and greenhouse gas emissions, at the same time as attempts are being made to produce sufficient food for the world?s increasing population. I ssues relating to efficient water use in agriculture are rarely accompanied by economic incentives (Hoekstra et al., 2009). For instance, the lack of actual economic value of water saving or loss in agriculture was also asserted by Zoebl (2006 ) . W ater footprint calculation based on hypothetical crop and water use ( Maes, 2009) and failure of growers to pay for diffuse discharge limit economic water scarcity resolutions. Issues relating to efficient crop cultivars are also challenged by social and political acceptance as well as pests and disease infestation. Sometimes such crops may have low economic value, low yields or poor taste despite being efficient in resource use. These shortfalls greatly limit the adoption of water saving concepts. Consequently, normal WUE indicators may not easily apply to such unanticipated water demand. This is the reason why the WUE concept requires integrated techniques and tools, in order to support CHAPTER TWO Literature Review 33 decisions relating to water allocation for specific crops and locations (Bessembinder et al., 2005) , such as those found in New Z ealand. Integral techniques offer more accurate results to counteract the challenges and limitations to optimization of WUE in potato, especially with the recent outbreaks of Tomato Potato P syllid (TPP) . 2.5.5 Tomato Potato Psyllid Tomato Potato Psyllid (TPP) ( Bactericera cockerelli ) is a new pest for potatoes and tomatoes that arrived in New Zealand in May, 2006 from North America (Thomas et al., 2011) . TPP is a vector of bacterium pathogen ? Candidatus Libaribacter solanacearum? which causes Zebra chip disease in potato (Thomas et al. , 2011) . TPP causes great challenges and limitations to maximisation of WUE in modern and heritage potatoes in New Zealand because of its devastat ing impact on tuber yield and quality ( Teulon et al., 2009). Teulon et al. (2009) and Pukehuke, (2010) stated that there is a substantial economic yield loss being caused by TPP in modern potatoes, tomatoes and Taewa. TPP attack reduces tuber number, tuber size and production of se condary tubers in potato and therefore reduces economic yield if not properly controlled. Studies on the biological and chemical control of TPP in New Zealand are promising to find a means of controlling TPP. The natural biological agents includes Micromus tasmaniae and Melanostoma fasciatum (Walker et al., 2011) while Tamarixia trizae (Burks) was introduced as biological agent from Mexico, (Workman & Whiteman, 2009). Page et al. (2011) found abamectin + oil and bifenthrin as effective pesticides for reducing adult TPP up to 3 days after treatment while thiacloprid, spiromesifen, imidacloprid, spinetoram and azadrachtin were found to be slightly toxic. However, Page et al. (2011) recommended that TPP nymphs are best controlled with abamectin + oil, s pirotetramat, bifenthrin and spiromesifen. In an earlier study by Berry et al., (2009) TPP nymphs were recorded dying 48 h after spraying with dichlorvos, lambda - cyhalothrin, methomyl, taufluvalinate, methamidophos and abamectin while applications of azadi rachtin, spiromesifen, abamectin, spirotetramat and thiacloprid gave 82- 100% mortality, while buprofezin, pymetrozine and imidacloprid application gave 36- 53 % mortality after 168 h. An integral point of TPP biological and chemical control is monitoring TPP populations, and the control of further introductions by New Zealand Government (Walker et al. 2011) . CHAPTER TWO Literature Review 34 2.6 Summary and conclusion The literature review shows that WUE is either expressed as a generic term for appraising water saving technologies (water footprint), or as a specific key indicator for appraising crop water productivity: that is, biomass per volume of water used or cash per volume of water used. Water use efficiency, expressed in a specific term also known as CWP , does not estimate environmental pollution (grey water components), whilst a water footprint, as the generic WUE indicator, estimates environment pollution (grey wa ter) and water consumption from surface or ground (blue water) and from rainfall (green water). A water footprint and EWP can be easily applied to the assessment of water savings of different crops in different locations, whilst crop water productivity can be used to compare crop cultivars of the same crops under different water management regimes. However, WF and CWP are both influ enced by climate factors, crops or cultivars and water management. The literature review has found few studies on economic water productivity relating to potato production. Consequently, strategies for maximising WUE in agriculture have not been accompanied by economic incentives. These strategies are based on physical output per volume of water used, rather than economic output per volume of water used for production. In view of this situation, the adoption of WUE strategies may encounter challenges, due to a lack of economic incentives. The review also indicates that crop cultivars with high efficiency in water use can improve generic and specific WUE, by enhancing the IWUE or ET -Yield slope, whilst efficient scheduling and an efficient irrigation system can improve WUE, by minimising water loss, that is, irrigation efficiency. It has also been reviewed that high NUE depends on an adequate amount of water, restricted N and cultivars, but it is currently challenged by the way in which agronomic, crop physiological features and genetic features can be combined, in order to achieve resource use efficiency, at plant and in the field. W ater use efficiency in potato depends on the plant?s water system called a Soil -Plant - Atmospheric Continuum, which varies with crop physiological and genetic features. The SPAC is controlled by stomatal and non-stomatal factors, in response to the atmosphere and soil environment. In turn, the atmospheric and soil environmental demands act as the regulatory components of potential crop evapotranspiration or crop water requirement (ET p), apart from the crop stomata. It has been reviewed that the potential ET for New Zealand is i ncreasing with climate change. Irrigation water requirements will increase due to high anticipated potential ET for New Zealand. The consequence of increased ET p on agriculture has an economic water scarcity effect rather than a physical water scarcity effect, since it will increase the costs of production and environment management. This CHAPTER TWO Literature Review 35 observation illustrates the significance of integrating both economic and physical water productivity appraisal in recommendations for future WUE strategies. There are opportunities available to reduce the impact of economic water scarcity, through improved WUE (correct water and nutrient management, pest and disease management and selection of appropriate crop cultivars). The review has also shown that many studies have been undertaken on N and irrigation in modern potato in New Zealand and other countries, but combined studies on heritage and modern crop response to irrigation and N management have never been undertaken, despite its uniqueness. The effects of water, N and leaf canopy management practices, reported in other glasshouse and field studies worldwide, necessitated a full exploration (in the context of WUE in Taewa) at glasshouse and field level. There is evidence that efficient water, N management and HI improve ment can increase Taewa production for small-scale farmers in New Zealand. The generic and specific WUE information relating to Taewa and other heritage crops, such as oca and Kamokamo, is important for the majority of farmers, who are extending their crop diversification to other neglected vegetables, which can earn them more profits than seasonal vegetables. Physiological WUE, (based on photosynthetic capacity), tuber or fruit yield and WUE based on dollar value, together with quality properties (tota l and reduced sugar, specific gravity), for Taewa and modern potato, are required to be studied further, in order to support crop diversification within the New Zealand agricultural industry. Lack of information on physiological WUE and tuber yield for heritage cultivars, in comparison to modern crop cultivars, contributes to the wide gap of tuber yield between Taewa and modern potato cultivars. It is probable that the high yield and WUE reported in modern cultivars is a result of previous studies, which ha ve led to improvement in management. Potato breeding has definitely increased tuber yield in modern potato. The high premium value of heritage cultivars, in relation to modern cultivars, also deserves further research for it to survive water scarcity (wate r costs increase and decline in water availability). CHAPTER TWO Literature Review 36 CHAPTER THREE Glasshouse Study 37 CHAPTER 3 COMPARISON OF WATER AND NITROGEN USE EFFICIENCY OF TAEWA AND MODERN POTATO CULTIVARS IN A GLASSHOUSE2 3.1 Introduction Taewa or Maori potatoes are heritage potato cultivars, which have been used by Maori for 200 years ( Roskruge, 1999) . The supply of Taewa to its niche market in the cultural economy is generally restricted by low yields (Harris et al., 1999; McFarlane, 2007) . This is a consequence of insufficient scientific research and published agronomic work on Taewa. For example, t here is scarce information available to Taewa growers on the benefits of irrigation and nitrogen management. This situation is in contrast to modern cultivars, which are typically produced on a large scale, mostly for domestic consumption either as table or processed potatoes. There is substantial evidence that potato yields are influenced by water and soil nutrient availability and genotypes (Belanger et al., 2002; Bowen, 2003) . Taewa growers need to be able to manage inputs such as fertiliser and irrigation, in order to reduce water loss and N leaching that both reduce profits and also result in adverse environmental effects. The application of the concept of water and nitrogen use efficiency can help farmers optimise resource use and maximise profitability ( Hoekstra et al., 2007) . A preliminary study was conducted on the performance of Taewa under modern production systems, with a focus on how they differ from modern cultivars in water and nitrogen use, at plant level. In the case of this preliminary study, a glasshouse offered a uniform environment for screening water and nutrient use traits ( Sumanasena, 2003) . The aim of the glasshouse experiment was to compare the physiological and morphological characteristics, in addition to water and nitrogen use efficiency in Taewa and modern potato cultivars, which were subjected to different levels of irrigation and nitrogen fertiliser. 2 Part of chapter 3 is published as: Fandika, I.R Kemp, P.D., Millner, J.P and D.J. Horne (2010) Water and nitrogen use efficiency in modern and Maori potato cultivars, Agronomy New Zealand, 40(2010). CHAPTER THREE Glasshouse study 38 3.2 Material and Methods 3.2.1 Location and plant establishment The experiment was located in a glasshouse at the Plant Growth Unit, Massey University, Palmerston North, from 23 June 2009 to 11 November 2009. Taewa cultivars, Moe Moe ( Solanum tuberosum ssp. tuberosum L .) and Tutaekuri ( Solanum tuberosum ssp. andigena Juz. & Buk.) and modern cultivars, Moonlight and Agria ( S. tuberosum ssp. tuberosum L .) were planted on 23 June 2009. Taewa seed tubers were from Maori Resource C entre whilst modern potato seed tubers were obtained from a potato seed company, Morgan Laurenson Ltd. Seed tubers (one per bag) were planted in 15 l plastic planting bags, which were partially filled with 10 l of air- dried sieved (2 mm) soil: the soil type was Manawatu sandy loam, a recent alluvial soil. The soil propert ies were: pH 5.4, Olsen P 36 mg kg - 1 , available nitrogen (N) 76.81 mg kg - 1 and K 86.02 mg kg - 1 . The soil bulk density was 1.35 g cm- 3 and the volumetric soil water content, at field capacity and wilting point, were 0.35 and 0.17 m 3 m- 3 , respectively. The planting bags were arranged in a square grid pattern spaced at 70 cm (Fig.3.1). The glasshouse temperature was regulated between 15 ?C and 25? C for the entire period. 3.2.2 Treatments and experimental design The experiment was laid out as a 2 * 2 * 4 factorial experim ental design with four replicates (two water regimes, * two N rates, * f our potato cultivars). In addition, eight bags were planted with Brassica napus L. (two per replicate) which was selected as a reference crop, due to its high potential water use for m onitoring actual evapotranspiration ( Wright et al., 1995) . 3.2.2.1 Irrigation and nitrogen fertiliser treatments Irrigation treatments were based on reference crop evapotranspiration (ET o) , implemented by applying 60 ET% (I 1 ) and 100% ET (I 2 ) every four days, up to day 77 after planting and subsequently, every two days. Irrigation to replenish the planting bags to field capacity was determined by weighing the B. napus L reference bag before and after irrigation, to obtain the mean ETo within the irrigation interval. The two N fertiliser application rates were 0.70 g N bag - 1 or (50 kg N ha - 1 ) and 2.8 g N bag - 1 or (200 kg N ha - 1 ) as urea. Urea was diluted to a concentration of 14 gl - 1 in water and applied manually in split application as basal dressing and top dressing. CHAPTER THREE Glasshouse study 39 Figure 3. 8 Layout of planting bags in the glasshouse CHAPTER THREE Glasshouse study 40 3.2.2.2 Plant protection All potato plants in the glasshouse were sprayed fortnightly, by hand, with TARATEK 5F fungicides (250 g litre- 1 chlorothalonil and 250 g litre- 1 thi- ophanate methyl), in order to control late blight. CHESS R WG (500 g kg - 1 pymetrozine) and ORTHENE WSG (970 g litre- 1 acephate) insecticides were applied to control potato aphids ( Macrosiphum euphorbiae Thomas), whitefl y ( Bemisia argentifolii Bellows & Perring ) and Solanum psyllid ( Bactericera cockerelli Sulc ). A number of Tutaekuri plants displayed symptoms (leaf curling and yellow ing) of potato leaf roll virus infection ( Roskruge 2009 Pers. Com.). Consequently, all the Tutaekuri plants were scored for severity of symptoms, on a scale of 0 - 5 (Table 3.1). 3.2.3 Crop physiological and soil moisture measurements 3.2.3.1 Vegetative growth characteristics Vegetative growth characteristics, recorded on the 100 th day after planting, were the number of stems per plant; plant height; stem diameter; number of compound leaves per plant; viral foliar diseases; canopy cover (%); leaf area index (LAI); and specific leaf area (S LA) . Leaf area was measured using a leaf area meter (Model 3100 Area Meter) and LAI was calculated as the total leaf surface area per unit ground area. After oven drying and weighing the leaf samples, the SLA ( cm2 g- 1 ) was determined as a measure of leaf thickness, by dividing leaf area per plant by leaf dry weight per plant (Amanullah et al., 2007; Vile et al., 2005) . Leaf dry matter content (g g - 1 ) was determined by dividing leaf dry weight per plant by leaf fresh weight per plant ( Vile et al., 2005) . Leaf canopy (being the spatial arrangement of the above - ground organs) was determined using K cp 1 equation for plant coverage : ???1 = ?? ?? ? 100, ( Ertek et al., 2006) , where W p is the plant canopy width (cm) and W b is the pot spacing (cm). 3.2.3.2 Photosynthetic water use efficiency and gaseous exchange Photosynthetic water use efficiency (?mol CO 2 /mmol H 2 O), defined as how efficiently the potato plant obtained carbon dioxide for photosynthesis, with a given amount of water, was determined as the ratio of net photosynthesis (A n) to transpiration rate (T) ( Xu & Hsiao, 2004; Liu et al., 2006a) . CIRAS - 2, a portable photosynthesis system (V2.01), was used to measure A n ( ?molCO 2 m 2 s- 1 ); T (m molH 2 O m 2 s- 1 ) ; leaf stomata CHAPTER THREE Glasshouse study 41 conductance (m molCO 2 m 2 s- 1 ) ; internal CO 2 concentration (ppm); a nd leaf vapour pressure deficit (bars), between 1000 - 1200 hrs, on newly expanded leaves (3 rd leaf on main axis). Photosynthetic active radiation ( ?mol photons m 2 s- 1 ) and reference CO 2 (ppm) were respectively maintained at an average of 1400 and 400, during all the CIRAS measurements. Measurements took 1 - 2 minutes per plant. Gaseous exchange was measured four times, between 20 and 90 days after plant emergence (DAE). 3.2.3.3 Soil moisture content 9.5 l of water was applied uniformly in each planting bag, for both irrigation treatments, up to day 50 from planting (Fig. 3.2). Irrigation scheduling, which was later based on the reference crop, Brassica napus, determined the remainder, in order to obtain the total cumulative evapotranspiration for the treatments, from planting to harvesting (Fig.3.2). The volumetric s oil moisture content in the bags was measured weekly, usi ng a time- domain reflectometer (TDR, mo del 1502C, Tektronix Inc., Beaverton, OR, USA) . 3.2.4 Tuber yield, water and nitrogen use efficiency Harvesting was undertaken once, after physiological maturity on 11 th November, 2010. The number of tubers per plant, individual tuber weight (g) and total tuber weight (g), were measured. Water use efficiency (WUE) was determined as the total tuber yield (g), per unit of water used ( l bag- 1 ) . N itrogen use efficiency (NUE) was determined as the total tuber yield (g), per unit of N applied per bag (g N bag - 1 ) (Darwish et al., 2006) . 3.2.5 Specific gravity and tuber dry matter content After harvesting, ten potato tubers were randomly selected from each planter bag , to be used for tuber dry matter content (DM) and specific gravity (SG ) determination (Plate 3.1) . The samples were thoroughly washed and dried before weighing. The expression of SG was determined by weighing the potato in air and in water (Haase, 2003; S mith, 1975) , using Mettler PJ3600 Delta Range scale, to two decimal places (Plate 3.1) . The specific gravity was calculated using the following equation: Specific gravity = Weight of tuber in Air (Weight of tuber in Air?Weight in water ) Equation 3.1 CHAPTER THREE Glasshouse study 42 The DM was determined by oven drying chopped potato at 70 oC, until the change in DM was constant, which was soon after determining its SG . The initial and final weight, for each sample, was measured and the DM% was calculated, by dividing the final dry weight by the initial fresh weight and then multiplying it by 100. Additionally, DM% and starch (%) w ere predicted, using regression models (Haase, 2003). 3.2.6 Statistical analysis The data on soil moisture, physiological and morphological characteristics, tuber yield and yield components measurements and water and nitrogen use efficiency, were analysed with the General Linear Model (GLM ) procedure of the Statistical Analysis System (SAS) (SAS, 20 08) and differences amongst treatment means were compared by the Least Significant Difference test (LSD ) at 5% probability (Meier, 2006) . Pearson correlation analysis was used to determine the relationship between tuber yield and crop water use and photosynthetic WUE and gaseous exchange parameters. CHAPTER THREE Glasshouse study 43 Description : Large bucket was filled with water and small bucket with potato . Small bucket was tied with chain hanged on scale. Small bucket containing potato was being floated in large bucket to determine specific gravity. Plate 3. 1 Measurement for specific gravity and sample of Moe Moe, Tutaekuri , Moonlight and Agria tubers Moe Moe Tutaekuri Agria Moonlight CHAPTER THREE Glasshouse study 44 3.3 Results 3.3.1 Evapotranspiration and soil moisture content (%) 3.3.1.1 Cumulative evapotranspiration from planting Figure 3. 9 Total irrigation accumulated after planting in the glasshouse Total cumulative evapotranspiration was 28.6 l and 43.7 l for the 60% ET and 100% ET irrigation treatments, respectively (Fig. 3.2). The cumulative irrigation ( l /bag) increased throughout the growing period. The trend portrayed by the reference crop enabled adjustments to keep the experimental crop well watered, throughout the experimentation period (Fig. 3.2). 3.3.1.2 Volumetric soil water content (%) Volumetr ic soil moisture content was strongly influenced by cultivar (P<0.05), irrigation (P<0.0001), and N (P<0.0001), between 20 and 85 days after planting. Cultivars and the irrigation regime differences were observed from days 20 to 85, whilst the N regime had a significant effect between days 71 and 85 (P<0.0001, P<0.05) (Fig. 3.3, Appendix 3.1). Interactions between cultivars and irrigation (P<0.01 ) were recorded for days 57 to 71. CHAPTER THREE Glasshouse study 45 Figure 3. 3 (a) Interaction between irrigation and cultivar on volumetric soil moisture content (%) during the experiment period. Error bar represents LS D at 5%. Figure 3. 10 (b) C hange in volumetric soil moisture content (%) for each cultivar over time. Error bar represents LSD at 5%. CHAPTER THREE Glasshouse study 46 The interaction was a result of an increase in water extraction by Moe Moe, whereas Moonlight and Agria decreased water extraction, compared to Moe Moe within this period (Fig. 3.3b). Plant water extraction from the soil increased with plant growth (Fig. 3.3). 100% ET had higher volumetric soil content than 60% ET (Fig. 3.3a). Amongst the four cultivars, Tutaekuri extracted the least water, from day 20 to 85, whilst the remaining cultivars did not differ in soil moisture content (P>0.05) (Appendix 3.1). 3.3.2 Vegetative growth characteristics in four potato cultivars 3.3.2.1 Potato seed size, days after emergence (DAE) and flowering production The average tuber weight of the seed potatoes at planting was significantly different, with a range from 25.20?7.01 (g) to 99.58?11.97 (g) (P<0.0001, Table 3.1). The modern cultivars, Agria and Moonlight, had a larger seed tuber than Tutaekuri and Moe Moe. Days to emergence differed amongst the cultivars (P<0.0001). Moonlight, followed by Agria, was the earliest cul tivar to emerge, whilst the Taewa cultivars, Tutaekuri and Moe Moe, were the last to emerge. Table 3. 1 Mean potato seed tuber weight (g), days to emergence, flowering, disease scores at 0 - 5 scale and leaf features . Note: Column rows with same letters are not significantly different, LAI is average leaf area index and SLA is specific leaf area at physiological maturity. CHAPTER THREE Glasshouse Study 47 3.3.2.2 Flower production and physiological maturity Days from date of emergence, to date of 50% flowering, differed between potato cultivars (P<0.0001; Table 3.1) . Moe Moe had the shortest duration to flowering: it flowered 37 days after emergence, whilst the last to flower, Agria, flowered after 52 days (Table 3.1). Days to flowering in all cultivars were not affected by irrigation and N (P>0.05). All four cultivars were harvested on 11 th November 2010, 14 1 days from planting. 3.3.2.3 Average number of stems per plant Moonlight had the greatest number of stems per plant, followed by Agria: Agria was not different to Moe Moe, but it was greater than Tutaekuri (P<0.000 1, Table 3.2). Irri gation and N had no effect on the number of stems per plant (P>0.05). The number of stems per plant were affected by an irrigation*N interaction (P<0.05) and an irrigation*N*cultivar interaction (P <0.05), in addition to a cultivar*irrigation interaction (P <0.05, Table 3.2). The interaction effects were not consistent in all the cultivars. Irrigation and N increased stem number per plant, in Agria and Moe Moe, but it reduced stem numbers in Moonlight and Tutaekuri (Table 3.2). 3.3.2.4 Average plant height ( cm) Moe Moe was the tallest cultivar, whilst Moonlight was the shortest cultivar (P<0.0001, Table 3.2). The plant heights for Agria and Tutaekuri were not different from each other. Irrigation and N had no effect on plant height, but there was interaction between N and irrigation (P<0.05 ). This interaction was caused by an increase in plant height under 60% ET with N increase and a plant height decrease with N increase under 100% ET. 3.3.2.5 Average stem diameter (mm) Tutaekuri had the largest stem diameter, whilst Moonlight had the smallest stem diameter (P<0.0001, Table 3.2). The stem diameter for Agria and Moe Moe were not significantly different (P>0.05). There was a significant irrigation and N regime interaction on plant stem diameter (P<0.05) caused by an increase in stem diameter under 60% ET with N increase, whilst it decreased with N increase under 100% ET. CHAPTER THREE Glasshouse Study 48 Table 3. 2 Potato characteristics on number of stems per plant, plant height (cm) and stem diameter (mm) in the glasshouse, 2009 CHAPTER THREE Glasshouse Study 49 3.3.2.6 Leaf morphological characteristics and diseases Moe Moe had high leaf numbers per plant: significantly greater than Moonlight and Agria (P<0.0001) (Table 3.1). Plant canopy (%) was not affected by cultivars. Tutaekuri had a higher LAI than the other cultivars (P<0.00 01). Moonlight had a higher SLA than all the other cultivars (P<0.05). Tutaekuri was significantly affected by potato leaf - roll virus (characterised by the rolling of leaves, leaf curling, yellowing and stunted growth), whilst none of the other cultivars displayed any symptoms (P<0.0001). 3.3.3 Photosynthetic water use efficiency and gaseous exchange in the glasshouse 3.3.3.1 Photosynthetic water use efficiency (?mol CO 2 /mmol H 2 O) in four potato cultivars Figure 3. 11 Photosynthetic WUE for different potato cultivars*DAE. Error bar represents ?SEM. Photosynthetic WUE (?mol CO 2 /mmol H 2 O) was significantly influenced by potato cultivar (P<0.0001) and DAE (P <0.01) (Table 3.3). On average, Moe Moe and Tutaekuri had the highest photosynthetic WUE. Mean photosynthetic WUE was l owest CHAPTER THREE Glasshouse study 50 on day 50 and highest on day 20, although there was no statistical difference between days 65 and 85 (Table 3.3, Fig.3.4). 3.3.3.2 Net photosynthesis (?molCO 2 m 2 s- 1 ) of four potato cultivars Net photosynthesis (A n) significantly differed between cultivars (P <0.000 1), irrigation (P<0.0001), N regimes (P<0.0001) and DAE (P <0.0001, Table 3.3, Appendix 3.2) . Taewa (particularly Moe Moe) had the highest average A n throughout the growing period, except for day 20, when Agria had the highest average An ( Appendix 3.2) . Net photosynthesis tended to decrease from day 20 to 85 (P >0.0001, Table 3.3). On average, An was highest on day 20, except in Moe M oe, which was highest on both day 20 and 50 ( Appendix 3.2) . There was an interaction between DAE*cultivars (P <0.001, Appendix 3.2) and potato cultivar*irrigation*N (P <0.05) for A n. High irrigation and high N increased A n in modern cultivars, whilst it decreased it in Taewa, with the largest reduction being in Tutaekuri (Fig.3.5; Appendix 3.2a ). Figure 3. 12 Interaction between irrigation, nitrogen and potato cultivars on A n in the glasshouse, 2009. Error bar represents ?SEM. CHAPTER THREE Glasshouse study 51 3.3.3.3 Stomatal conductance (m molCO2 m2 s - 1) of four potato cultivars Stomatal conductance (g s ), significantly differed with cultivar (P <0.05), N ( P<0.01) and DAE (P <0.0001, Table 3.3). The g s significantly increased up to day 65 and then decreased, under both irrigation and N treatments (Appendix 3.2b). N itrogen enhanced gs whilst irrigation influence was observed on day 50 (P <0.05). In most cases, the modern cultivar, Agria, had the highest gs, whilst the Taewa (particularly Moe Moe ) , had the lowest gs. 3.3.3.4 Transpiration rate (m molH2O m2 s - 1) of four potato cultivar Transpiration rates (T ) were influenced by cultivar (P <0.05) and DAE ( P<0.0001, Table 3.3). Agria had the greatest T, whilst Moe Moe had the lowest T. The maximum T , for almost all cultivars, was on day 50, when irrigation had a significant effect on T and the lowest T was on day 85 ( P<0.05). The general trend was that the cultivar with the highest gs also had the highest T and lower An. 3.3.3.5 Internal CO 2 concentration (Ci) and vapour pressure deficits (VPD) Moonlight and Agria had the greatest Ci , whilst Taewa had the lowest Ci (P <0.0001, Table 3.3). Vapour pressure deficit was high in Moonlight, although it was not different from Tutaekuri and Moe Moe, but it was higher than A gria, which was lowest in VPD (P <0.001). Irrigation signific antly reduced leaf VPD and Ci (P <0.0001) , whilst N d id not affect VPD or Ci (P <0.0001) (Table 3.3). 3.3.3.6: The relationship of photosynthetic WUE to gaseous exchange variables The relationship between photosynthetic WUE and other gaseous exchange variables was explored, by using simple cor relation (Table 3.4). With all the data combined, there was a correlation between photosynthetic WUE and T (r = 0.58, P <0.00 01); g s (r = - 0.45, P <0.0001) ; leaf temperature (r = - 0.46, P <0.0001); A n (r = 0.35, P<0.0001); Ci (r = - 0.45, P <0.0001) and V PD (r = - 0.012, P >0.05). When data were stratified by cultivars, a moderately strong negative (P <0.000 1) correlation was identified with T, leaf temperature, gs and Ci, in all cultivars. The correlation between Ci and T was very strong in the modern cultivars, c ompared to Moe Moe (Table 3.4). CHAPTER THREE Glasshouse study 52 Table 3. 3 Photosynthetic WUE (PWUE) and gaseous exchange in four potato cultivars in the glasshouse, 2009 Note: Column rows with same letters are not significantly different, C = cultivar, N=nitrogen, I=irrigation, DAE = day after emergence. When stratified by irrigation, photosynt hetic WUE was strongly correlated (P <0.0001) to T, g s , leaf temperature, A n, Ci; 60ET% (r = - 0.52, r = - 0.42, r = - 0.35, r = 0.31, r = 0.31, r = - 0.02); and 100% ET (r = - 0.68, - 0.58, - 0.58, 0.039, - 0.66), respectively. Data stratified by N analysis revealed a correlation between photosynthetic WUE and T, gs , leaf temperature, A n, Ci; low N (P <0.0001) (r = - 0.62, - 0.53, - 0.48, 0.31, - 0.28, 0.05) and high N (P <0.0001), (r = - 0.52, - 0.41, - 0.41, 0.45, - 0.72) , respectively . There were no correlations between photosynthetic WUE and VPD. CHAPTER THREE Glasshouse study 53 Table 3. 4 Photosynthe tic WUE relationship with A n, T and g s, leaf temperature (LT), Ci, leaf VPD in four potato cultivars 3.3.4. Tuber yield response to irrigation and N regime in four potato cultivars The number of tubers per plant, mean tuber weight and total tuber weight were strongly affected by cultivar (P <0.0001, Table 3.5). Irrigation (P<0.0001 ) and N (P <0.01) increased the total tuber yield per plant, but it did not influence the number of tubers per plant and mean tuber weight. Increased irrigation, from 60% ET to 100% ET, increased the total tuber yield per plant in all the cultivars. Tuber yields were increased by 35%, 30%, 57% and 41%, for Moonlight, Agria, Tutaekuri and Moe Moe, r espectively. Similarly, N also increased total tuber yield per plant in Moonlight, Agria, Tutaekuri and Moe Moe, by 16 %, 10%, 8% and 10 %, respectively. Nitrogen responses in low irrigation were generally less than those for high irrigation (Table 3.5). There were significant interactions between cultivar and irrigation treatments on the number of tubers per plant (P<0.01) and mean tuber weight (P <0.01) (Table 3.5 and Fig. 3.6). Significant interactions were also observed between cultivar, irrigation and N, on tuber numbers per plant (P <0.05) and total tuber weight per plant (P <0.01) (Fig. 3.6). The interaction involving tuber yield resulted from the decrease in yield, at the high N and 100% ET irrigation in Tutaekuri, whereas in the other cultivars high N and 100% ET did not reduc e yield. In contrast, high N incr eased yield at 60% ET while decreasing at 100% ET in Tutaekuri (Fig. 3.6). The mean tuber weight and total tuber yield per plant, in Agria, were higher than all the other cultivars, whilst Moe Moe had the highest number of tubers per plant. Cultivars PWUE*T PWUE* An PWUE*g s PWUE*Ci PWUE*LT PWUE*VPD Moonlight r = - 0.60, r = 0 .57 r = - .045 r = - 0.77 r = - 0.31 r = 0.04 P<0.0001 P<0.0001 P<0.001 P<0.0001 P<0.05 P>0.05 Agria r = - 0.78 r = 0.28 r = - 0.64 r = - 0.57 r = - 0.38 r = 0.00 P<0.0001 P>0.05 P<0.0001 P>0.0001 P<0.05 P>0.05 Moe M oe r = - 0.38 r = 0.20 r = - 0.26 r = - 0.27 r = - 0.17 r = - 0.09 P<0.01 P>0.05 P<0.05 P<0.05 P>0.05 P>0.05 Tutaekuri r = - 0.73 r = 0.17 r = - 0.58 r = - 0.30 r = 0.12 r = - 0.3 P<0.0001 P>0.05 P<0.0001 P<0.05 P>0.05 P>0.05 Note: An = net photosynthesis; T = transpiration rate; g s = stomatal conductance; VPD = l eaf vapour pressure deficit; Ci = internal carbon concentration and PWUE = p hotosynthetic water use efficiency CHAPTER THREE Glasshouse Study 54 Table 3. 5 Yield response to irrigation and nitrogen regime in four potato cultivars under glasshouse conditions. CHAPTER THREE Glasshouse Study 55 Figure 3. 13 Interaction between cultivars, irrigation and nitrogen regime on total tuber yield (g/bag). Error bar represents ?SEM. 3.3.5: Water use efficiency and nitrogen use efficiency of four potato cultivars Water use efficiency reflected tuber yields and it was highest in Agria, which was significantly (P <0.0001 ) higher than Moonlight and Moe Moe (Table 3. 6). Water use efficiency of Tutaekuri was significantly lower than for all the other cultivars. Water use efficiency was also affected by irrigation and N in all cultivars , except Tutaekuri . Increasing irrigation, from 60% ET to 100% ET, reduced WUE by 12% in Moonlight, 15% in Agria and 9% in Moe Moe (Fig. 3.7). The high N fert iliser rate increased WUE by 15 % in Moonlight, 9 % in Agria, 8 % in Moe Moe and 19% in Tutaekuri (Fig. 3.7). However, high N increased WUE at 60%ET while decreasing WUE at 100%ET (Fig. 3.7) Similarly, NUE was significantly higher (P < 0.0001) for Agria than Moe Moe and Moonlight, which were significantly higher than Tutaekuri. Nitrogen use efficiency was significantly affected by irrigation (P<0.0001) and N fertiliser (P <0.0001). There was a significant interaction between irrigation and N (P <0.0001) and between irrigation, N CHAPTER THREE Glasshouse study 56 and cultivar (P<0.05) on NUE (Fig. 3.8 and Table 3.6). Increased irrigation increased NUE by 30% in Moonlight, 26% in Agria, 33% in Moe Moe and 104% in Tutaekuri. However, high N reduced NUE by 67% in Moonlight, 68% in Agria, 70% in Tutae kuri and 69% in Moe Moe. The relationship between WUE and NUE was explored using a simple correlation. With all data combined, no correlation between WUE and NUE was found. However, when data were stratified by N treatments, moder ately strong (P <0.01) correlations were identified: low N (r = 0.71) and high N (r = 0.72). Data stratified by irrigation analysis revealed no correlation between WUE and NUE. Figure 3. 14 Interaction between cultivars, irrigation and nitrogen regime on WUE (g/ l). Error bar represents ?SE M. CHAPTER THREE Glasshouse study 57 Figure 3. 15 Interaction between cultivars, irrigation and nitrogen regime on nitrogen use efficiency (NUE) (kg/gN). Error bar repres ents ?SEM. CHAPTER THREE Glasshouse Study 58 Table 3. 6 Water use efficiency (WUE) and nitrogen use efficiency (NUE) in four potato cultivars. CHAPTER THREE Glasshouse Study 59 3.3.6 Specific gravity and tuber dry matter content in four potato cultivars Specific gravity and DM % were significantly affected by cultivar (P <0.05), but not by irrigation and N ( Table 3. 7, Appendix 3.3). Moe Moe had the highest SG and DM %, whilst Moonlight had the lowest SG and DM %, respectively. Significant interactions were observed for DM % b etween cultivars*irrigation*N (P <0.001) and irrigation*nitrogen (P <0.01). Appendix 3.3 shows that high N, with high irrigation, decreased DM %, compared to high N with low irrigation. The interaction between cultivars*irrigation*N on DM % was very prominent for Tutaekuri ( Appendix 3.3 ) . The predicted starch content (%) was also highest in Taewa, although it was not significantly different from the modern cultivars (P> 0.05). Specific gravity, amongst all cultivars, was highly positively correlated with the DM %. The SG and DM% relationship in the modern cultivar was linear, whereas the SG and DM% relationship in Taewa was curvilinear ( Appendix 3.4) . Agria DM % = 178.1(S G) - 170.64 R? = 0.49; Moonlight DM% = 206.3(S G ) - 201.7, R? = 0.91; Moe Moe tDM% = - 3696.1(S G) 2 + 8249.2( S G) - 4576.1, R? = 0.85 and Tutaekuri DM % = - 1638.2(S G) 2 + 3726.7(S G) - 2091.2, R? = 0.94 ( Appendix 3.3) . Measured DM % also had a moderately strong correlation with predicted starch content and predicted DM % (r = 0.66, P<0.0001). The cultivars with high SG, that being Taewa, had increased DM % and predicted starch content (Table 3. 7, Appendix 3.3 ; Appendix 3.4). CHAPTER THREE Glasshouse study 60 Table 3.7 Specific gravity and tu ber dry matter content of four potato cultivars in glasshouse experiment Note: Column rows with same letters are not significantly different. CHAPTER THREE Glasshouse study 61 3.4 Discussion 3.4.1 Evapotranspiration and volumetric soil water content The results of this study show that Moonlight, Agria and Moe Moe extracted more soil water than Tutaekuri. This indicates potato cultivar differences in water extraction under different soil moisture regimes. Although the replacement of 100% evapotranspir ation supplied adequate soil moisture to maintain field capacity, Tutaekuri gradually extracted less soil moisture. Consequently, the other three cultivars extracted more water from a greater depth within the low irrigation treatment, compared to the well watered conditions. The availability of water, the health state of plant and growth stages are the factors that influence soil water use within the soil profile (Stalham et al., 2004) . The ability of Tutaekuri to extract water may have been reduced by a potato leaf- roll viral disease (PLRV) infection that reduced its vigour (Ovenden et al., 1985). Leaf curling and chlorosis caused by PLRV might have affected leaf water use and root water uptake in Tutaekuri . 3.4.2 Vegetative growth characteristics of Taewa and modern potato cultivars 3.4.2.1 Potato seed size and days to emergence Taewa had small seed tubers which were late to emerge compared to the modern cultivars. The differences in emergence could be due to cultivar differences in dormancy or sprouting, as a response to low temperatures experienced during the winter (Mustonen, 2004) . Potato cultivars differ in dormancy: those with the longest dormancy period are reported to be the latest to sprout (Bogucki et al., 1980) . Nevertheless, seed size and days to emergence hardly affected yield and yield components in this study, whereas other studies have reported low production (Wiersema et al., 198 6) and delayed emergence due to small seed (Mustonen, 2004) . This result suggests that the difference in tuber seed size is probably due to genetics, rather than environmental conditions. On the other hand, germination was due to genetics and environmental factors interactions. Taewa might have longer dormancy compared to modern cultivars. The low temperatures in winter might have increased the dormancy in Taewa unlike modern cultivars which are bred to suit different environmental conditions. CHAPTER THREE Glasshouse study 62 3.4.2.2 Vegetative growth characteristics Taewa cultivars were tall with a large leaf canopy, whilst the modern cultivars were shorter with a smaller leaf canopy. The large leaf canopy and leaf area in Taewa coincides with other findings in wheat ( Siddique et al., 1990a ) , soya bean (Frederick et al., 1991) and oats (Ziska et al., 2007), which concluded that heritage cultivars have greater vegetative growth than modern cultivars. Contrary to other reports, N and irrigation had little effect on other growth characteristics and flowering (Manochehr et al., 2009) . Moe Moe flowered earlier than the modern cultivar, Agria. This result suggests that the cultivar effect was greater than N or the irrigation ? s influence on vegetative growth characteristics within the glasshouse. 3.4.3 Photosynthetic WUE and gaseous exchange in Taewa and modern potato Photosynthetic WUE and gaseous exchange were strongly influenced by cultivar, irrigation, N and DAE in this study, supporting earlier reports in potatoes ( Ghosh et al., 2000; Vos et al., 1989a; Vos et al., 1987) . However, high N decreased A n in Taewa, whilst it increased in the modern cultivars. Photosynthesis increased with irrigation increase in all cultivars, except Tutaekuri, which had high A n at low irrigation. The high An in Taewa, compared to modern cultivars, may be due to the genotypic variation in stomatal and mesophyllic activity as also observed in old and modern Durum wheat by Ko? et al. ( 2003) . Taewa does not require a high amount of N for A n maintenance. Nevertheless, optimal water is a requirement in Moe Moe and the modern potato for maximum gas exchange (Olesinski et al., 1989) . Photosynthetic WUE and A n initially increased before declining with time in all cultivars, regardless of irrigation and N treatment. A similar result has also been reported by Ghosh et al. (2000). Figures for photosynthetic WUE and A n were remarkably high from days 20 to 50. Generally, modern potatoes had high An within the first three weeks from emergence, but Taewa high A n was extended up to 65DAE ( Appendix 3.2). The tendency for photosynthetic WUE and A n decrease was greatest in the modern cultivars, Agria and Moonlight, possibly due to early maturity, compared to Taewa ( Appendix 3.2) . Ghosh et al. (2000) also reported high An within 20DAE and concluded that this period had raised An due to tuberisation. Moorby (1970) also reported a rise in An with tuberisation in potato. In this study, Taewa delayed tuberisation, hence their extended high gaseous exchange. CHAPTER THREE Glasshouse study 63 Taewa, achieved high photosynthetic WUE by maintaining high A n at low gs, T and Ci, compared to Agria and Moonlight ( Appendix 3.2) . Taewa and Moonlight had comparable gs and T. However, A n and photosynthetic WUE, in Moonlight and Agria, steadily reduced with water stress. The main driver of these differences was Ci, which was high in the modern cultivars and low in Taewa. Photosynthetic WUE is negatively correlated with Ci, particularly in modern cultivars. Consequently, its increase in modern cultivars reduced An and photosynthetic WUE. This finding agrees with other studies, which have indicated that increased C i reduces An (Morison, 19 98) . For this reason, Taewa differ from modern potato cultivars in photosynthetic WUE, in the way Ci manipulates stomata apertures. It is possible that modern cultivars have changed gaseous exchange behaviour through breeding ( Morison, 1987) , t hereby resulting in disparity in photosynthetic WUE with heritage cultivars. Heritage cultivars have not undergone several breeding processes so gaseous exchange has not been modified (Vos et al., 1989a) . Water deficit increases leaf VPD, which consequen tly reduces gs and photosynthetic capacity (Malti et al., 20 02) . In this study, the A n, g s and T increased with irrigation and N, whereas VPD and Ci declined with irrigation. It was also observed that VPD was significantly influenced by water deficit, thus resulting in low An and photosynthetic WUE . This shows that reduced irrigation, below optimal levels, affects gaseous exchange in both Taewa and modern potato cultivars ; although this differs. Nevertheless, Taewa exhibited exceptionally high photosyntheti c WUE characteristics under water stress. This ability suggests they are well adapted to low water supply. 3.4.4 Total tuber yield, water and nitrogen use efficiency Moe Moe responded to irrigation and N primarily through an increase in tuber numbers, whereas Agria responded by producing few tubers with increased tuber weight. Increased yield, in response to irrigation and N, results from increased partitioning of assimilates to the roots and tubers, but the influence on yield components can vary with the cultivar (B?langer et al., 2002) . The manipulation of irrigation and N enhances potato tuber yield through increased tuber numbers (MacKerron et al., 19 86) and tuber weight, but the mechanism varies with cultivar (Fig. 3.6 and Table 3.5). CHAPTER THREE Glasshouse study 64 The relatively poor yield of Tutaekuri, at 100% ET and high N, may have been the result of a virus infection in the plants used in this treatment combination (Ovenden et al., 1985) , as a result of infected seed tubers (Roskruge, pers . comm. 2010). The virus symptoms were present in Tutaekuri, whereas no virus symptoms were observed in the other cultivars. Consequently, manipulat ion of the environment may not affect yield and WUE in all genotypes ( Steyn et al., 1998) . Fo r this reason, growers need to consider all factors, including disease control, when seeking optimum resource use to maximise their profitability, because high WUE depends on these factors ( Jefferies et al., 1993b; Vos et al., 1989b) . Mean WUE varied with yield and it ranged from 13.1 g l - 1 (Agria) to 6.4 g l - 1 (Tutaekuri). This equates to 7.6 and 15.6 l , respectively, to produce a 100 g tuber and it is lower than an estimate of the mean global virtual water content of 25 l for a 100 g potato tuber (Hoekstra et al., 2007). Irrigation and plant growth in the glasshouse was well controlled and this might have influenced lower virtual water content, rather than the mean global virtual content, which was estimated in the field . Water use efficiency was highest under restricted irrigation, but a consequence of this situation was that NUE was reduced. Wang et al., (2009b) also reported that WUE was higher in partial root- zone drying and deficit irrigation, rather than that found i n well watered potato crops, when full irrigation, partial root - zone drying and deficit irrigation were compared in a glasshouse environment. The integration of management utilises the correlation between WUE and NUE reported in this and other studies (Battilani et al., 2004) . The adoption of high yielding cultivars can be based on selecting cultivars with high WUE and high NUE, in addition to high soil water abstraction. In this study, tuber yield and WUE were relatively high in the three cultivars and WUE was affected by the irrigation regime, whereas the low yielding cultivar (Tutaekuri) had low WUE, irrespective of the irrigation level. This result suggests that manipulation of the environment might not affect yield and WUE in potato cultivars with l ow potential yield, so much as that in cultivars with a high potential yield (Steyn et al ., 1998) . Tuber yield response to irrigation was greater than that of N . The requirement for adequate water in potatoes has been well documented (Ferreira et al., 20 07) , whereas high rates of N can decrease the yield for potatoes (Manochehr et al., 2009) . During sunny days, the temperature in the glasshouse was generally above 20 oC and this suggests that evapotranspiration (and therefore the requirement for irrigati on water CHAPTER THREE Glasshouse study 65 estimated by Brassica napus ) was adequate, especially when the potatoes were in full canopy. This result is supported by the high water extraction of soil moisture, by Agria, Moonlight and Moe Moe between days 20 and 50 (Fig.3.3). Moe Moe showed similar productivity and resource use efficiency to Moonlight and Agria, despite the fact that it is a heritage cultivar. This result agrees with the suggestion that high tuber yield and WUE, which is apparent in most modern cultivars, relies on a combination of factors, including appropriate site selection, pest and disease control and the optimum management of inputs, rather than simple genetic improvements, in order to achieve high yield and WUE ( Richards et al., 2002; Barker et al., 2003) . The performance of Moe Moe indicates that, with appropriate management of inputs, its use may allow growers to access high value niche markets (McFarlane, 2007) , without necessarily suffering low yields. 3.4.5 Specific gravity and tuber dry matter content The values of SG, as a measure of DM in potato, are influenced by genotypes, environment and their interaction ( Killick et al., 1974; Jefferies et al., 1993 b; Kellock et al., 2004) . In this study, SG was not strongly affected by irrigation and N , but it was influenced by genotypes. The possible reason for this result may be that the moisture and N availability met the potato crop requirements (B?langer et al., 2002) . Taewa had high SG and DM, compared to the modern cultivars. Similar result has been previously reported by Singh et al. (2008), who found that Moe Moe (1.069, 21.9 % ,) and Tutaekuri ( 1.074 21.6%) had higher SG and DM, than the modern cultivar, Nadine. However, the SG in Moe Moe and Tutaekuri, in this study, was very high compared to results reported by Kellock et al. ( 2004) and Verma et al., ( 1971) . Genetic factors and the late maturity of Taewa may increase the period of dry matter accumulation (Ki llick et al., 1974). Tutaekuri demonstrated that irrigation and N increases would steadily decrease DM ( Appendix 3.3). This interaction is paramount for the use of SG in tuber quality determination in Taewa, because appendix 3.4 shows that SG is a surrogate trait to DM in tuber quality ( Kellock et al., 2004). These genotypi c differences in tuber quality are essential for modern production systems, because they can be used to set standards of input management in Taewa and they can also provide genetic resources for improving CHAPTER THREE Glasshouse study 66 modern potato processing quality. It is apparent th at Taewa growers need to be aware of how they manipulate the soil moisture and N environment, in order to maintain a high level of tuber quality. 3.5 Conclusion This study compared vegetative growth and gaseous exchange characteristics, yield and yield components, WUE and NUE , in Taewa and modern potato cultivars that were subjected to two different levels of irrigation and N, in the glasshouse. It was observed that Taewa had wide and tall stems with a large leaf canopy, whilst the modern cultivars had a prominent number of short stems with a small leaf cannopy. Photosynthetic WUE and An differed between cultivars and it decreased with time, regardless of irrigation and N treatment: with the highest photosynthetic WUE and A n being observed in Taewa. It was also observed that Taewa had high DM and SG, compared to the modern potato cultivars. The results also indicate that irrigation and N application improves Taewa and modern potato cultivars? yields. Total tuber yields were highest in Agria and Moe Moe: and this was a result of the high mean tuber weight and high tuber number per plant, respectively. Increased water supply increased yield and NUE, but it decreased WUE. Cultivars with high WUE also had high NUE. Subsequent field studies, on the same cultivars, will provide a more detailed insight into the effect of different water regimes on Taewa and modern potato cultivars, in relation to their physiological characteristics, yield , WUE and NUE . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 67 CHAPTER 4 COMPARISON OF MODERN AND HERITAGE POTATO, OCA AND PUMPKIN SQUASH CULTIVARS? RESPONSE TO IRRIGATION AND RAINFALL IN THE FIELD 4.1 Background The glasshouse experiment results in C hapter 3 indicated substantial differences in yield and WUE between some Taewa and modern potato cultivars. The yield response to an increase in irrigation (60 % ET to 100% ET) suggests that, in the field, irrigation c ould affect heritage and modern crop cultivars differently. Therefore, further understanding of water use in Taewa and modern potato cultivars ( Solanum tuberosum ssp. Tuberosum L and Solanum tuberosum ssp. andigena Juz. & Buk.) and other heritage crops , whe re there is renewed commercial interest, such as oca or New Zealand yam ( Oxalis tuberosa Mol.) and pumpkin squash, Buttercup squash ( Cucurbita maxima Duchesne .) and Kamokamo (Cucurbita pepo L inn) in the field is crucial. However, no field study has been conducted to quantify and compare the yield- water use functions and water footprint of Taewa and modern potato and oca and pumpkin squash cultivars, under irrigation in New Zealand . The field experiment reported in this chapter was conducted in order to measure and compare yield, physiological characteristics and water use efficienc y indicators ( irrigation water use efficiency, economic water productivity and water footprint ) of heritage and modern potato, oca and pumpkin squash cultivars , under rain- fed and irrigation in the field in New Zealand. The change of production, from crop enterprises with low water productivity to enterprises with high water productivity, would reduce the water footprint at farm level, in addition to increasing profits. 4.2 General materials and methods 4.2.1 Experimental site The field experiment was conducted at Massey University?s Pasture and Crop Research Unit, Palmerston North, commencing on 10 th November 2009. The site is located at a latitude of 40 o 22. 54.02 S, longitude 175 o 36 ? 22.80 E, and an altitude of 36 m above CHAPTER 4 Field experiment on potato, oca and pumpkin squash 68 sea- level. The soil type is Manawatu sandy loam . There were 106 kg ha - 1 of available N and 76.8 mg N kg - 1 of soil anaerobically mineralised N at the beginning of the experiment. Other soil chemical characteristics (Ols en P, K, organic matter content, and pH) for the paddock are shown in Table 4.1. The maximum and minimum temperature and rainfall collected by the metereorology station for the site during the season is presented in Fig . 4.1.1. Table 4.1 Soil chemical characteristics: pH, applied nitrogen (N), Olsen phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na) and cation exchange capacity (CEC) for the site as of 10 th November, 2009 4.2.2 Experimental layout and crop management The experiment, which consisted of four potato cultivars ( Solanum tuberosum L., Solanum tuberosum ssp. andigena Juz & Buk.), two oca or New Zealand yams ( Oxalis tuberosa Mol.) and two pumpkin squash varieties ( Curcubita pepo Linn and C ucurbuta maxima Duchesne) was laid out as a split - plot design, with water regimes as the main plots (rain - fed and irrigation treatments) , each being randomised and replicated four times. The crop cultivars were subplots. The four potato cultivars were two modern cultivars (Agria and Moonlight ( S. tuberosum L.) and two Taewa [Moe M oe ( S. tuberosum L.) and Tutaekuri ( S. tuberosum ssp. andigena Juz & Buk.)]. The two pumpkin squash cultivars were buttercup squash, Ebisu (C . maxima Duchesne , a modern cultivar) and a heritage pumpkin cultivar, Kamokamo ( C. pepo Linn ,), whilst two unnamed oca cultivars with dark orange and scarlet coloured tubers (both heritage cultivars) were used. Each crop cultivar was replicated four times pe r water regime and eight times in the entire experiment (Fig . 4.1). Amongst the potato cultivars, Moe M oe has a multi- coloured skin with creamy patterned flesh whilst Tutaekuli has long- yam- like tubers with dark purple f lesh, both with haulms maturing in 160 - 180 days (Harris et al., 1999; Hayward, 200 2) . Agria and Moonlight are dual - purpose main- crop potato cultivars with haulms maturing in 140- 150 days (Anderson et al., 2004, Plate 3.1) . Taewa seed tubers were from Maori R esource Centre whilst modern potato seed tubers were obtained from the potato seed company, ? Morgan Laurenson Ltd? . Certified Buttercup squash seed were sourced from CHAPTER 4 Field experiment on potato, oca and pumpkin squash 69 ? Massey Seed Technology ? section while certified Kamokamo seed was purchased from ? Kings Seed Compa ny? . Oca seed tubers were locally sourced from a New Zealand farmer. 4.2.3 Plot-size and plant spacing Potato tubers were manually sown on 10 th November, 2009, at 75 cm spacing between rows and 40 cm spacing within rows at a depth of 10 - 15 cm. Each plot was 6 m by 1.5 m and each plot held 30 plants. Each plot had two guard rows planted with the Desiree variety. Oca was also manually sown on 10 th November 2009, in rows spaced at 75 cm and with 35 cm between seed tubers, with one tuber per station, in a 10 - 15 cm deep furrow that was opened by machine. The gross plot was 6 m by 3 m and the net plot was 6 m by 1.50 m, each with 34 plants. Pumpkin squash cultivars were manually sown on 9 th December, 2009 at a spacing of 75 cm between rows, with 60 cm between plants and one plant per station, at a depth of 25 mm. Each plot ( 4.5 m by 6 m) had four rows of 6 m each, with 10 planting stations (Plate 4.1, Figure 4.1) . 4.2.4 Fertiliser application and plant protection The potatoes and oca received 12N:5.2P: 14K: 6S +2Mg+5C a, using 500 kg Nitrophoska Blue TE at planting and this was followed by 100 kg N ha - 1 of urea, as a side dressing, on 15 thDecember 2009. The pumpkin squash received 12N:5.2P:14K: 6S +2Mg+5C a, using 700 kg ha- 1 Nitrophoska Blue TE at planting, followed by 66 kg N ha - 1 , as a side dressing, on 19 th January 2010, when the vines started running. Mounding was done once during the season, when the plants had reached about 15 - 20 cm height ( McKenzie , 1999) . Weeds w ere initially managed by pre- emergence herbicides and secondary weeds were manually controlled. Leopard herbicide with 100 gl- 1 Quizalofop- P- ethyl active ingredients and 812 gL - 1 hydrocarbon liquid as a solvent was applied at 500 ml ha- 1 to control couch grass also known as Elymus repens ( Cynodon dactaylon). G esagard 480SC herbicide with 480 gL - 1 Prometryn and 1, 2- benzisothiazolin- 3- one at 0.019% was applied as a preservative at 3.75 L ha- 1 to control other annual broad- leaved weeds, using 100 - 200 litres of water per hectare. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 70 Chlorothalonil Tetrachloroiophthalonitrile (Bravo ULTREX SDG90), a broad spectrum fungicide, was sprayed in a mixture with 600 g/litre Methamidophos (Metafort 60S L), which is an organo- phosphorus insecticide, in order to control funga l diseases and insect pests; powderly mildew ( Erysiphe cichoracearum, Jaczewski); early blight ( Alternaria solani, Ellis & G. Martin ) and late blight ( Phythophthora infestans, Mont .); bacterial diseases ( Pseudomonas solancearum, Smith); potato pest insects ; potato psyllid ( Bactericera cockerelli Sulc ); potato aphids ( Macrosiphum euphorbiae, Thomas); and potato tuber moth ( Phthorimaea operculella, Tomohiro Ono) in potato and pumpkin squash. Metafort 60S L was sprayed at 800 ml ha- 1 , in 500- 1000 litres of water per hectare, every 14 days. 4.2.5 Irrigation system and irrigation scheduling 4.2.5.1 Irrigation system The Trail T150 - 2 traveller irrigator (Plate 4.1 a), with a 52 mm * 100 m angus premium Hi - Flow hose pipe and a minimum pull at 582 kPa (70 psi), was installed in the paddock, for an irrigation block system of 6 m width each side (Fig.4.1). The irrigator tapped water from the main supply line through a long polythene pipeline that was connected to its hydrant. The irrigator was running on a 2 m wide irrigation lane between two blocks and it applied water to 6 m on either side (Fig. 4.1) . Each arm of the irrigator consisted of four low pressure sprinkler s (10 psi), with a sprinkler nozzle diameter of 16 m, thus giving triple coverage in order to improve uniformity. The design application depth for the irrigator is approximately 40 mm hr - 1 . How ever; the irrigator?s speed was adjusted to 6 m hr - 1 to give an actual application depth, per pass, of 25 mm. The water supply for the entire field was controlled at the hydrant, whilst for each treatment it was controlled through valves on the irrigator. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 71 Figure 4. 1 Schematic diagram of the 1 st field experiment layout [ horizontal s cale 1:300 and vertical scale 1:400] CHAPTER 4 Field experiment on potato, oca and pumpkin squash 72 4.2.5.2 Crop water use and soil moisture measurement A soil water balance was used to determine the soil moisture deficit (SMD) on a daily basis during the growth of the crops (Premrov et al., 2010). The potential evapotranspiration (ETp) in the soil water balance was computed for crops using the FAO 56 Penman - Monteith method ( Allen et al., 1998; Kassam et al., 200 1) . The crop coefficient factors used in the crop water use computation were for potato, because this was the most sensitive crop to water use (Shock et al., 2007) . The daily weather data, for running the soil water balance model, were collected we ekly from NIWA/AgResearch climate site, Palmerston North. The soil water balance was used to schedule irrigation events and to calculate the quantity of drainage (D p ) over the growing period. The irrigation treatment was based on refilling 25 mm of the so il?s moisture deficit (SMD) on the day that soil moisture deficit equated or exceeded 30 mm. This schedule was based on supplying approximately half the ?readily available water? held by the soil at the site, Manawatu fine sandy loam. The actual crop evapotranspiration (ET c ) was determined using equation 4.1 ( Allen et al., 1998) . Soil moisture change (?S) was the difference between soil moisture content at the end and the start of the field experiment as measured using a Time- Domain Reflectometer [TDR, model 1502C, Tektronix Inc., Beaverton, OR, USA] In addition to measuring soil water content at the start and conclusion of the trial, it was also monitored before irrigation and 24 hours after irrigation to a depth of 50 cm. As the site was flat and the crops were in the ground for the summer/autumn period, surface runoff (R o ) can be ignored. ETc = P + I - D p - R o+ ?S Equation 4.1 The total crop water use or consumption water use (CWU) for the entire growing cycle, for irrigation and rain- fed treatments, were referred to as blue and green components, respectively. The CWU was determined according to Hoekstra et al. (2009), as in equation 4.2: Where ?????????? and ?????? ??????? is the accumulation of actual water use (evapotranspiration) over the complete growing cycle for irrigated and rain - fed crops, respectively. Factor of 10 is required to convert water depths of mm into volume in m3 ha- 1 ( Hoekstra et al., 2009). CWU blue+green = 10 * ?ETcblue + ETcgreen Equation 4.2 CWUgreen = 10 *?ETgreen CHAPTER 4 Field experiment on potato, oca and pumpkin squash 73 4.2.6 Morphological and physiological characteristics measurements 4.2.6.1 Vegetative growth characteristics of Taewa and modern potato cultivars During the 2009 /2010 field trial, leaf features (the number of compound leaves per plant, LAI, S LA ( cm2 g- 1 ), canopy cover and leaf dry weight per plant were measured at 32, 72, 95 and 128 days after emergence (DAE). The plant height (cm); number of stems per plant; number of branches per plant; and stem diameter at soil collar (m m), were measured after 100 days from planting. The LAI, leaf dry matter content (LDMC), S LA and crop canopy were measured according to Amanullah et al. (2007), Vile et al. (2005) and Ertek et al. (2006), as presented in Chapter 3. 4.2.6.2 Photosynthetic water use efficiency and gaseous exchange Gaseous exchange was measured four times between 20 and 90 days, in potato and oca, after plant emergence, using CIRAS - 2 (a portable photosynthesis system V2.01) (Plate 5.1a) . L eaf stomata conductance (m molCO 2 m 2 s- 1 ) ; net photosynthesis (?molCO 2 m 2 s- 1 ); transpiration rate (m molH 2 O m 2 s- 1 ); internal CO 2 concentration (ppm); leaf vapour pressure deficit (bars) and l eaf temperature (C o) were recorded between 1000 - 1200 hrs, on newly expanded leaves (3 rd leaf on main axis). Photosynthetic water use efficiency (Photosynthetic WUE) (?molCO 2 /m molH 2 O) was determined as the ratio of net photosynthesis to transpiration rate ( Xu & Hsiao, 2004; Liu et al., 2006b). Photosynthetic Active Radiation (?mol photons m 2 s- 1 ) and reference CO 2 (ppm) were respectively maintained at an average of 1400 and 400, during all the CIRAS measurements. The measurements took 1 - 2 minutes per plant. 4.2.6.3 Leaf w ater potential of Taewa and modern potato cultivars Leaf water potential ( ?w) was measured in potato using the Scholander pressure chamber method [Soil Moisture Equipment Corp., Santa Barbara, CA, USA] on both irrigated and non- irrigated plants (Boyer 1995; Plate 5.1b) . It was measured at 2:00 pm, two days after irrigation application. A leaf to be measured was cut out using a scalpel, and then partly sealed in the pressure chamber. The chamber was pressurised with compressed gas until the distribution of water by the living cell and the xylem appeared on the open end of the xylem conduits: and the pressure used to release the droplets was then recorded (Boyer, 19 95). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 74 4.2.6.4 Dry matter production and partitioning characteristics in potato cultivars Above- ground (leaves and stems) and below - ground biomass (roots and tubers) were sampled before plant senescence. Samples were collected on 18 th February 2010, 100 days after planting. A small and a larger plant sample were randomly uprooted from each plot, using a spade. The plants were partitioned into leaves, stems, roots and tubers and then weighed and oven dried at 70 oC, until there was no more change in the dry matter content (DM ) (B?langer et al., 2001; Geremew et al., 2007) . The ratio of each partition to total biomass (leaves, stems, roots and tubers) per plant was determined. Root/shoot ratio was determined as dry weight for roots divided by dry weight of above- ground biomass (leaves +stems biomass) (Siddique et al., 1990b) . Harvest index was calculated as the ratio of total tuber yield to total biomass production on dry matter basis from the samples of each plot, 100 days after planting and again at the final harvest (Mackerron et al., 1985) . 4.2.6.5 Tuber growth and development measurements in oca Tuber development for oca was monitored 100 , 132, 154, 1 74 and 224 days after planting (DAP). One poor and one well developed plant sample were randomly uprooted from each plot using a spade and partitioned into shoots and tubers, before being dried in an oven for 72 hrs at 70 oC, in order to determine dry matter (B?langer et al., 2001). The tuber growth rate per day was determined as the ratio of tuber fresh biomass (g) and the number of days taken to accumulate tuber fresh biomass (Plaisted, 1957) . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 75 4.2.7 Final total yield and yield components measurements 4.2.7.1 Total yield and marketable yield for oca, potato and pumpkin squash Pumpkin squash (Buttercup and Kamokamo) were harvested on 29 th and 31 st March 2010, respectively. At harvest, fruit yield (kg); the number of fruits per plant; individual fruit weight; fruit yield; and total biomass were measured. Pumpkin squash fruits were graded into marketable and non- marketable grades (NM): marketable fru it was above 1kg, without any damage and non- marketable were fruit <1kg and fruit with damage. Marketable fruit was further graded as S (1 - 1.2 kg), M (1.2- 1.4 kg), L (1.4- 2.5 kg) and XL (>0.2.5kg), where S is small, M is medium, L is large and XL is extra - large, according to export quality grades in New Zealand by Leaderbrand Produce Limited . ( http://www.leaderbrand.co.nz/Buttercup_Squash_(Kabocha)55.aspx) Potato was harvested on 17 th May, 2010, whilst oca was harvested on 22 nd June, 2010. At harvest, the total fresh tuber yield (kg); marketable tuber yield; number of tubers per plant; and average tuber weight per plant were measured. Potato and oca tubers were later graded into marketable and non - marketable grades. Oca marketable tubers were above 12.5 g, without any damage and non- marketable tubers were <12.5 g and tubers with damage. Marketable tubers were further graded as medium (M) (12.5 - <25.0 g) and large size grade (L) (>2 5 g), according to marketable quality grades in New Zealand (Osborne, 2010 Pers. Com.,). Potato marketable tubers were those above 55 g, without any damage and non- marketable were those <55 g and those with damage (Roskruge & McFarlane, 2010 Pers. Com.,) . Marketable potato tubers were not further graded. At harvest, shoot biomass (vines + leaves) was measured from five sample plants of each plot in potato, oca and pumpkin squash. Harvest index was calcula ted as the ratio of total tuber or fruit yield to total biomass production on dry matter basis, from the five samples taken from each plot (Mackerron et al., 1985) . The total biomass was the sum of dry harvestable yield and shoot biomass (vines + leaves). 4.2.7.2 Determination of specific gravity, DM a nd total sugars Specific gravity and DM of potato were determined on ten tubers according to Haase, (2003), as presented in Chapter 3 (Plate 3.1) . After SG measurements and DM CHAPTER 4 Field experiment on potato, oca and pumpkin squash 76 determination, total sugar was determined from the eight composite samples above. Potato samples of 0.5 g were taken from the outer equatorial portion of each tuber of the ten tubers, excluding the skin, giving 2.5 g fresh weight for composite samples for each experimental plot before sending them to Massey Animal Nutrition Labo ratory. The total sugars were extracted with aqueous alcohol and determined by using Pheno - sulphuric acid colorimetry at Massey Animal Nutrition Laboratory (Hall et al., 1999) . 4.2.8 Determination of efficient water use: key indicators 4.2.8.1 Irrigation water use efficiency and water stress factors Irrigation water use efficiency (IW UE) was defined as the total yield difference between irrigation (Y ns) and rain - fed (Y ds) divided by the net evapotranspiration from irrigat ed crops (I i) according to Howell, (2001). The IW UE was used for assessing contrasting crop cultivars? performance with increasing water use, using regression analysis (Ferreira et al., 2007). The IW UE equation 4.4 took into account the contribution of irrigation to yield production for each crop cultivar tested in this experiment (Howell, 2001): The effect of water stress on rain- fed crops was determined by a drought intensity index (DII) according to Ramirez - Vallejo et al., ( 1998) as DII = 1 - ??? ??? : Where Y ds is the mean experimental yield of all cultivars from the same crop grown under rain - fed conditions and Yns is the mean experimental yield of all cultivars from the same crop grown under irrigation (Ramirez - Valejo et al., 1998) . The DII >0.7 indicated seve re water stress. Geometrical mean yield was determined as GM = ??????? ? ?????? to predict cultivar performance under water stress and non- stressed environment (Ramirez - Vallejo et al., 1998; de Souza Lambert, 2006) . The yield reduction (PR %) due to water stress under rain- fed, in relation to the irrigated environment, was determined as PR% = { ??????? ??? ? 100%}, where Y sd and Y ns are the yield of a given cultivar in a rain- fed and irrigated environment, respectively (Ramirez - Vallejo et al., 1998) . Water stress factors such as geometrical mean, DII and yield reduction were used to determine genotypical variations under water stress and well watered environments ( Ramirez - Vallejo & Kelly et al., 1998; de Souza Lambert, 2006) . IWUE = ????????????? ???? Equation 4.4 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 77 4.2.8.2 Economic water productivity for heritage and modern crop cultivars The economic water productivity index (NZ$/m 3 ) was assessed as the overall present value of each crop?s marketable produce (NZ$) divided by the volume of water (m 3 ) consumed by the plant (Barker et al., 2003; Molden et al., 2001) . The average crop prices used were those supplied by ? Statistics New Zealand ? , (2010) ( http://www.stats.govt.nz ) and personal communication ( Osborne , 201 0) for oca . Kamokamo and Ta ewa prices were found at ? Pak & Save supermarket ? , Palmerston North ( 2010) and by personal communication (Roskruge, 2010). 4.2.8.3 Water footprint of growing heritage and modern crop cultivars The water footprint (WF) (m 3 tonne- 1 ), defined as the volume of water required to produce a given weight or volume of oca, potato and pumpkin squash (t ha - 1 ), in New Zealand, was determined as the ratio of consumptive water use (CWU m 3 ha- 1 ) plus grey water to the total crop yield (t ha - 1 ) according to Hoekstra et al., ( 2009). The total water footprint is the sum of blue (irrigation), green (rainwater) and grey water footprint s. The blue and green water footprint (m 3 tonne- 1 ) was a ratio of blue and green crop water use (mm) to the total yield, respectively (Mekonne n et al., 2010a b) . The blue plus green water footprint was referred to as the consumptive water footprint (Chapagain et al., 2005). Grey water i s the additional water required to dilute or attenuate any fertiliser and pesticide pollution to an acceptable level in the receiving water body (Clothier et al., 2010). The grey water footprint (m 3 tonne- 1 ) was determined as the ratio of the total volume of water (m 3 ) required for diluting N that is leached, per tonne of produce (Chapagain et al., 2005) . The grey water footprint was estimated by multiplying the leaching fraction by the applied N (kg ha - 1 ) and dividing the difference between the permissible limit and natural concentration of N in the receiving water body (Hoekstra et al., 2009) . This study assumed a natural water nitrate concentration of 5.6 milligrams per litre and a permissible limit of 11.3 milligrams per litre (Daughney et al., 2009) . The leaching fraction of the 160 kg and 150 kg ha - 1 applied N , for potato or oca and pumpkin squash cultivars, was assumed to be 10 - 15% (Chapagain et al., 2005, Mekonnen et al., 2010a ) . The study compared the water footprint based on actual crop yield and crop water use, in order to remove the disparity of over - estimation, when hypothetical crop and crop water requirements are used (Kumar et al., 2007; Maes, 2009) . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 78 4.2.9 Statistical analysis The data on physiological characteristics, total fresh tuber or fruit yield and marketable yield, were initially analysed separately for each crop. Subsequently, crop water use and total yield from the three crops were pooled, in order to determine their comparative irrigation water use efficiency, the stress indicator s, water footprint and economic water productivity. The data was analysed by the GLM procedure of the SAS (SAS, 2008) and differences amongst treatment means were compared by the LSD , at 5% probability (Meier, 2006) . The RCBD split - plot linear statistical model used in GLM procedure was as follows: ?ijk = ? + ? i+? j +(??)ij +? k +(??)ik +(??) j k +(???)ijk +?ijk ; Where, ? is the overall mean, ? i , ? j , (??)ij represents the whole plot as irrigation, block and whole plot error effects; ? k , (??)ik , (??) j k represents subplots as cultivars? effects, block effects and subplot errors; (???)ijk represents whole plot and subplot interaction effects; and ?ijk represents overall error, respectively, whilst i= 1 - 2 water regimes, j=1 - 4 replicates and k=1 - 8 crop cultivars. 4.3 Results The results and discussions for this chapter are presented in four sections, which cover the physiological characteristics and yield response of Taewa and modern potato (Section 4.3.1), oca ( S ection 4.3.2) and pumpkin squash ( S ection 4.3.3) to irrigation. Finally, there is a comparison of key water use efficiency indicators in heritage and modern potato, oca and pumpkin squash (S ection 4.3.4) . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 79 (a) Potato, oca and pumpkin squash on blocks irrigated by travel irrigator and others non irrigated (b) Pumpkin squash plot (c) Oca plot Plate 4 .1 : Irrigation and heritage and modern crop cultivars layout at field level in 2009/ 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 80 SECTION 4.3.1 TAEWA AND MODERN POTATO CULTIVARS? RESPONSE TO IRRIGATION AND RAIN-FED CONDITIONS 4.3.1.1 Introduction Potato production and yields have expanded in New Zealand and in the Pacific region, due to the introduction of modern varieties, improved cultivation, market access and differences in consumer preferences ( Pandey, 20 08) . It is a subject of debate whether the potato yield increase is really a consequence of breeding or agronomic practices ? or their interaction, or part thereof. L ow yields and yield erosion of old potato cultivars are some of the reason that these cultivars are being substituted by modern cultivars ( Solanum tuberosum) ( Harris et al., 1999) . This is also happening with other heritage crops, such as Brassica napus ssp. Napobrassica (Gowers et al., 2006) , w heat (Siddique et al., 1990a ) and soybean (Frederick et al., 1991) . Regardless of substantial advancement in modern potato production, other quality traits for Taewa have attracted the interest of growers and consumers (McFarlane, 2007 ; Lambert, 2008) . The results reported in this section are on Taewa physiological and morphological characteristics, tuber yield and WUE compared to modern potato cultivars under irrigation and rain- fed conditions in the field. 4.3.1.2 Materials and methods All details of Taewa and modern potato experiment methodologies are presented in the general methodology section 4.2 above. This section presents the results on plant physiological and morphological characteristics, tuber yield and WUE for Taewa and modern potatoes only. 4.3.1.3 Results 4.3.1.3.1 Crop evapotranspiration, precipitation and irrigation The growing season for Taewa and modern potato were 179 and 132 days, with a seasonal potential crop water requirement of 610 mm and 550 mm, respectively ( Appendix 4.1.1). Precipitation supplied 69% of the potential water requirement CHAPTER 4 Field experiment on potato, oca and pumpkin squash 81 ( Fig.4.1.1). The irrigated potatoes received 200 mm of irrigation water, which met at least 100% of the potential crop water requirement . The average crop water use for the rain- fed crop was 65.1% of the irrigated potato ( Appendix 4.1.1). Finally, crop water use for the modern potato cultivars was 91.6% and 88.6% of that used by Taewa under irrigation and rain- fed environment, respectively ( Appendix 4.1.1) . Figur e 4.1.1 Cumulative rainfall (mm), cumulative potential crop evapotranspiration (ET p) (mm), monthly average maximum and minimum temperatures ( ?C ) for the experimental site , during the experiment period from November 2009 to June 2010 4.3.1.3.2 Volumetric soil water content (%) S ince precipitation was not well distributed during the growing season, irrigation reduced the soil moisture deficit, (Fig. 4.1.2; Appendix 4.4.2). This was verified by the significant differences in the volumetric soil moisture content (%) between water regimes, crop cultivars and measure ment dates (P<0.0001). Volumetric soil moisture content (%) in rain- fed was lower and it ranged between 15 - 20%, whilst irrigated treatments ranged between 20 - 35% (Fig. 4.1.2). 0 5 10 15 20 25 30 35 0 100 200 300 400 500 600 700 800 Nov. Dec. Jan. Feb. March April May June Months Max & Min im um T em pe ra tu re (C o) C um ul at iv e Rai nf al l & ET p (m m ) Cumulative Rainfall (mm) Cumulative ETp (mm) Max. Temperature Min.Temperature CHAPTER 4 Field experiment on potato, oca and pumpkin squash 82 Figure 4.1.2 Volumetric soil moisture (%) change in Taewa and modern potato under irrigation and rain- fed conditions. Error bar represents ?SEM. 4.3.1.3.2 Vegetative growth characteristics of Taewa and modern potato cultivars 4.3.1.3.2.1 Flower production and physiological maturity Cultivars and irrigation did not statistically affect flowering (P>0.05 ; Table 4.1.1). Taewa and modern potatoes matured after 132 and 179 days from planting, respectively. 0 5 10 15 20 25 30 35 40 45 50 4 Jan. 7 Jan. 14 Jan. 5- Feb 22 Feb. 3- Mar 10- Mar 16- Mar 24- Mar 15- A pr 20- A pr 26- A pr 11 -May Vol um et ri c so il m oi st ur e (%) Days after plant emergence Agria - Irrigated Moe Moe -Irrigated Moonlight - Irrigated Tutaekuri-Irrigated Agria -Rainfed Moe Moe - Rainfed Moonlight - Rainfed Tutaekuri - Rainfed CHAPTER 4 Field experiment on potato, oca and pumpkin squash 83 Table 4.1.1 Vegetative growth and yield component characteristics of Taewa and modern potato cultivars under irrigation and rain- fed conditions in 2010. Measured at harvest except days to flowering. 4.3.1.3.2.2 Average plant height (cm) and number of main stems and branches per plant and Stem diameter (mm) Taewa cultivars were the tallest, whilst the modern cultivars were the shortest cultivars (P <0.0001; Table 4.1.1). Moe M oe was the tallest cultivar but similar to Tutaekuri. Moonlight was intermediate in height, whereas Agria was the shortest. I rrigated crops were significantly taller than rain- fed crops (P<0.05) . Moe M oe did not show a reduction in its height, following a water deficit, whilst the two modern cultivars had significantly reduced height, due to water stress (P <0.05). S tems and branch aggregates per plant were not influenced by irrigation: they were influenced by type of cultivar (P<0.05, P <0.001). Moonlight had the largest average number of stems per plant, the same as Agria (P <0.05 ). Agria and Moonlight had more main stems and fewer branches per plant than the Taewa cultivars. The number of branches on Taewa was twice that for CHAPTER 4 Field experiment on potato, oca and pumpkin squash 84 Moonlight : and more than ten times that for Agria ( Table 4.1.1 ). Taewa had the largest stem diameter whilst the modern cultivars had the smallest diameter, especially Agria (P<0.05, Table 4.1.1) . I rrigation had no significant effect on stem diameter (P> 0.05) ( Table 4.1.1) . 4.3.1.3.2.3 Leaf characteristics Leaf area index , leaf dry matter per plant (g), LDMC (g g - 1 ), and crop canopy (%), differed between potato cultivars and DAE (P <0.0001; Table 4.1.2). Irrigation had an effect on LAI, leaf dry matter per plant , canopy cover and LDMC ( g/g) (P<0. 01), but not on SLA (cm 2 g- 1 ) (P>0.05). Specific leaf area varied with time of plant growth (P<0.0001) , but not with cultivar and irrigation (P>0.05) . On average, Taewa cultivars were highest in these leaf features, except for LDMC (P<0.0001). Agria was the smallest value for these traits, except for LDMC, where it was the highest. Moonlight was intermediate in these traits (P<0.0001; Table 4.1.2). There were significant interactions between cultivar and DAE on leaf area, LAI, S LA, LDMC, leaf dry matter per plant and canopy cover (P<0.0001). The leaf trait above increased from emergence and they reached a peak almost at the same time for all cultivars, prior to their senescence after 95 DAE (P <0.0001; Table 4.1.2). It was observed that the crop canopy was mainly affected by cultivars , not the water regime, al though the highest was rain- fed Moe M oe, followed by irrigated Moe Moe and Tutaekuri (P <0.0001). Moonlight produced the highest canopy at the end, due to its delayed senescence, whilst the canopy decline in Agria was very drastic. Unlike the leaf area and canopy cover, the LDMC and SLA increased at an increas ing rate until senescence, when it was highest in Tutaekuri and Moe Moe, respectively . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 85 Table 4.1.2 Average leaf features of Taewa and modern potato cultivars under irrigation and rain- fed condition, 2009/ 2010 4.3.1.3.3 Photosynthetic water use efficiency and gaseous exchange 4.3.1.3.3.1 Photosynthetic water use efficiency (?molCO2/m molH2O) Photosynthetic WUE ( ?mol CO 2 /m molH 2 O ) significantly varied between water regimes (P <0.0001) and cultivars (P<0.001) and between measurement days (P <0.0001, Table 4.1.3, Appendix 4.4.4) . On average, Agria had the highest photosynthetic WUE, similar to Moe Moe ( Appendix 4.4.4). Photosynthetic WUE was significantly high under irrigation ( Appendix 4.4.4, P<0.05) . Photosynthetic WUE was lowest at Day 21 and it then increased to Day 48, followed by a decrease (P <0.0001; Appendix 4.4.4). Moe Moe had the highest photosynthetic WUE under rain - fed, at Day 48 (Appendix 4.4.4). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 86 Table 4.1.3 Gaseous exchange in Taewa and modern potato cultivars under different water regimes under field conditions, 2009/ 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 87 4.3.1.3.3.2 Net photosynthesis (?molCO2 m 2 s-1) of four potato cultivars N et photosynthesis (A n) significantly varied between potato cultivars, water regimes and DAE (P <0.0001, Table 4.1.3, Appendix 4.4.4). Appendix 4.4.4 shows that Agria and Moe Moe had the highest A n under irrigation and rain- fed conditions, respectively. The average seasonal An for the two cultivars did not vary (P>0.05). There was a consistent pattern of increasing and then decreasing An from early to later measurements ( P<0.000 1; Table 4.1.3). N et photosynthesis was greatest on D ay 48 in both irrigated and rain- fed potato ( Appendix 4.4.4; Table 4.1.3). 4.3.1.3.3.3 Stomatal conductance (m molCO2 m2 s-1) and transpiration rate (m molH2O m 2s-1) The gs and T only differed between measurement days, with the highest g s and lowest T on Day 48 in Moonlight (P<0.01, Table 4.1.3). Potato cultivars and irrigation had no significant effect on gs and T (P>0.05). 4.3.1.3.3.4 Internal CO2 concentration and vapour pressure deficits Internal CO 2 concentration was highest on Day 21 and lowest at Day 48 (P<0.0001), with no statistical differences between cultivars (P>0.05), but there was a difference between water regimes (P<0.0001). Irrigation significantly reduced Ci, whilst VPD only differed between DAE (P<0.0001) and not between cultivars and irrigation (P>0.05; Table 4.1.3). 4.3.1.3.4 Leaf water potential (?w) L eaf water potential (?w) was significantly influenced by the water regime (P <0.01) and not by cultivars (P >0.05; Table 4.1.4). The rain - fed plants had the lowest leaf water potential, compared to the irrigated plants . The potato cultivars were similar (P >0.05). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 88 Table 4.1.4 Effect of water regimes on leaf water potential (bars) in four potato cultivars, 2009/ 2010 4.3.1.3.5 Dry matter production and partitioning characteristics The average total dry matter production per plant measured 100 days after planting was not significantly different between potato cultivars and irrigation (P>0.05; Table 4.1.5, Plate 4.2). However, on partitioning of these plants into leaves, stems, roots and tubers, statistical differences emerged between cultivars (P <0. 05) . Irrigation had no significant effect on dry matter partitioning into leaves, stems and tubers (P >0.05) , except partitioning to the roots (P <0.05), (Table 4.1.5, Appendix 4.4.5, Plate 4.2) . Water stressed potato had highest root dry matter and root: shoot ratio was highest for Taewa (P<0.05). Taewa had more biomass in leaves, stems and roots , whilst modern cultivars had more tuber biomass per plant. Tutaekuri allocated > 37 % to leaves, >36% to stems and >8% of its biomass to roots, compared to Agria which translocated >60% to tubers and the least to leaves, stems and roots ( P<0.0001) ( Appendix 4.4.5; Table 4.1.5) . The trend of allocating assimilates in Moe M oe was followed by Tutaekuri , although it was not statistically different, whilst Moonlight was intermediate. Agria and Moonlight significantly partitioned differently in stems and tubers, but not in leaves and roots ( Table 4.1.5, Appendix Table 4.4.5) . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 89 Plate 4. 2 : A sample of fresh biomass partitioning per plant into leaves, stems, tubers and roots in two Taewa and two modern potato cultivars ( 2009/ 2010) CHAPTER 4 Field experiment on potato, oca and pumpkin squash 90 Table 4.1.5 Effect of water regimes on amount of leaves, stems, roots, tubers and total biomass on dry matter basis per plant (g) measured 100 days after planting , in four potato cultivars, 2009/ 2010 4.3.1.3.6 Tuber yield and yield components in Taewa and modern potato cultivars There were significant differences between irrigation and rain- fed potatoes on average tuber weight (P<0.001) , total tuber yield (P <0.0001) and marketable tuber yield (P <0.01; Table 4.1.6) . However, there was no difference between the number of tubers per plant and HI (P >0.05 ) , between irrigation and rain- fed potatoes. Irrigation enhanced the average tuber weight; fresh total tuber yield ; and marketable tuber yield , by 51%, 33% and 55% , respectively ( Table 4.1.6). Potato cultivars strongly influenced the number of tubers per plant; average tuber weight (P<0.0001); total tuber weight (P <0.0001); and marketable tuber yi eld (P<0.0001 ) and HI (P <0.0001) ( Table 4.1.6) . The highest number of tubers per plant was found in Tutaekuri and modern cultivars had the least, whilst Moe M oe was intermediate. Unlike the other two potato cultivars , Moe M oe and Agria had more tubers under rain- fed conditions. The average tuber CHAPTER 4 Field experiment on potato, oca and pumpkin squash 91 weight for modern potato cultivars were 1.7 times that of Moe M oe and almost 5.9 times that of Tutaekuri. The greatest average tuber weight was found in Agria, whilst Tutaekuri was the least. Mod ern cultivars did not differ in the number of tubers per plant and average tuber weight traits, whilst Taewa cultivars differed from each other (P <0.0001; Table 4.1.6). The water regime did not affect the number of tubers per plant in Agria and Moonlight : and neither did it affect both the number of tubers and the average tuber weight in Tutaekuri (P >0.05). Conversely, the number of tubers per plant in Moe M oe were reduced and there was an increase in the mean tuber weight with irrigation (P <0.001). Subsequently, the total fresh tuber yields and marketable tuber yields were not significantly different between Agria, Moonlight and Moe M oe, but they were all different to the lowest yielding, Tutae kuri, under both environments (P <0.0001). The tuber yields for Agria, Moonlight and Moe M oe were almost double that of Tutaekuri. The total fresh tuber yields and marketable tuber yields, for Tutaekuri, were not influenced by the water regime (P >0.05; Table 4.1.6). The behaviour of translocating assimilates to the harvested product was clearly demonstrated ( by the highest HI after 100 days from planting and at harvest) in Agria . Tutaekuri had the lowest HI whilst Moe M oe was intermediate ( Table 4.1.5, Table 4.1.6). The HI confirms that Taewa partitioned more dry matter to above- ground, whilst the modern cultivars partitioned more dry matter to tubers, as presented in Table 4.1.5, and Table 4.1.6. The water regime and cultivar interaction effects were observed on total tuber yield (P <0.01; Fig. 4.1.3). Th is interaction shows that irrigation increased total tuber yields in Agria, Moonlight and Moe Moe, but not in Tutaekuri . The effect of water stress was highly pronounced in Agria and Moonlight, whilst Moe M oe and Tutaekuri were somehow resistant to total yield reduction, a s a result of water stress ( Fig. 4.1.3). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 92 Table 4.1.6 Yield and yield components for Taewa and modern potato cultivars under irrigation and rain- fed conditions, 2009/ 2010 There was also a significant relationship between the number of tubers and the average tuber weight and HI at harvest. The number of tubers per plant were negatively related to average tuber weight (Average tuber weight (g) = - 1.6618 (Tubers plant - 1 ) + 110.29, R 2 = 66.3%) and harvest index (HI = - 0.0059 (Tubers plant - 1 ) + 0.8902, R 2 = 60.5%). The increase in the number of tubers per plant significantly decreased the average tuber weight and HI ( Appendix 4.4.6). The average tuber weight was also negatively related to plant height (r = - 0.52, P<0.01); number of branches per plant (r - = 0.60, P<0.01); stem diameter (r = - 0.32, P<0.05); and total fresh biomass per plant (r = - 0.63, P<0.001). In this case, Taewa?s vegetative growth and yield characteristics were related to a reduced average tuber weight in potato ( Appendix 4.4.6). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 93 Figure 4.1.3 Interaction between cultivars and water regime on total tuber yield (t ha - 1 ). 4.3.1.3.7 Water use efficiency for Taewa and modern potato cultivars Water use efficiency of total tuber yield was significantly influenced by the water regime and cultivars ( P<0.01; P<0.05; Table 4.1. 6). Rain - fed potato had high WUE . On average, Moonlight had the highest average WUE, although it was not significantly different from Moe M oe and Agria: but it was different from Tutaekuri ( P<0. 05). Tutaekuri did not differ from Agria in WUE under rain- fed regime. In addition, Moonlight did not differ from Moe M oe in WUE under rain- fed, but it did differ under irrigated conditions, with the highest being found in Moonlight ( Table 4.1.6 ). 4.3.1.3.8 Specific gravity , tuber dry matter content and total sugars Specific g ravity and DM (%) were significantl y different between cultivars (P>0.01, P<0.0001) but not between water regimes (P >0.05; Table 4.1.7). Tutaekuri had the highest SG and tuber DM (%), whilst Agria had the lowest SG and DM (%). Tutaekuri CHAPTER 4 Field experiment on potato, oca and pumpkin squash 94 was significantly different from all the cultivars in SG and DM%, whilst Agria and Moonlight were least in all traits. Moe M oe was intermediate in SG traits ( Table 4.1.7). Specific g ravity, within the four potato cultivars, was highly and positively correlated with the tuber dry matter content, DM ( % ) = 49.329 (SG) - 32.548, R? = 0.21, ( P<0.01) and percentage freeze- dried matter, percentage FDM = 53.043 (SG) - 35.16, R? = 0.16, P<0.05 (Fig . 4.3.6 ). Potato cultivars with high SG and thus, Taewa had increased DM % ( Table 4.1.7 and Appendix 4.4.7a ). Total sugars on freeze - dried matter basis and percentage of freeze - dried matter significantly differed between potato cultivars (P<0.01, P <0.0001) , but not between water regimes ( P<0.05; Table 4.1.8) . Moonlight had the highest total sugars, although it was not significantly different from Agria. However, they were both different from Moe M oe and Tutaekuri , which were least but not statistically different to Agria. Tutaekuri had a significant highest percentage freeze- dried matter content, which was different from all the potato cultivars, whilst Agria was similar to Moonlight. Moe M oe had an intermediate percentage freeze- dried matter amongst the four potato cultivars (Table 4.1.7). The total sugars on a freeze- dried matter basis negatively related to the percentage of freeze- dried matter or dry matter content (%), (P <0.05) and DM at harvest: but not to SG (P >0.05). However, the increase of both DM and SG decreased the total sugar content ( Appendix 4.4.7b). The equations for total s ugars? relationship with DM are: total sugars = - 0.0818(% FDM ) + 4.05, R? = 20; total sugars = - 0.0806 (D M %) + 3.91, R? = 0.13, whilst the equation for total sugars to specific gravity is t otal sugars= - 6.2185 (SG) + 8.9786, R? = 0.07, as presented in appendix 4.4.7b. The cultivars with high total sugars ( that is modern cultivars) had low DM (%) and SG (Table 4.1.7 and appendix 4.4.7). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 95 Table 4.1.7 Effect of water regime and cultivars on total sugars, percentage of freeze - dried matter, s pecific gravity and dry matter content, in 2009/ 2010 growing season 4.3.1.4 Discussion 4.3.1.4.1 Vegetative growth characteristics Taewa had more vegetative growth supported by few main tall stems with many branches, leaf area and large canopy, compared to modern potato cultivars. A similar trend has been observed in old wheat (Siddique et al., 1989). The increase in the number of leaves, leaf size and branches in Taewa could be associated with high radiation utilisation. On the other hand, the leaf features indicate that high vegetat ive growth in Taewa was accompanied by low LDMC , compared to modern cultivars. Wilson et al., (1999) studied LDMC and SLA and reported that LDMC is a more accurate predictor of how resources are captured and used in plants for growth. In the case of this study, modern cultivars appear to be able to efficiently utilise radiation resources, compared to Taewa. Siddique et al. ( 1989) found modern wheat cultivars to be more efficient in capturing radiation than old cultivars, despite large LAI. The high vegetative growth in old cultivars caused mutual shading and a high humid micro- climate, which resulted in low radiation use and low LDMC (Siddique et al., 1989). In both Taewa and modern cultivars , irrigation played a role in increasing leaf features, plant height and the partitioning to the roots, but not on the number of stems and branches per plant. Outstandingly, the overall vegetative growth characteristics were CHAPTER 4 Field experiment on potato, oca and pumpkin squash 96 greatly influenced by cultivar differences (Jefferies et al., 1993a b) . Taewa, despite early flowering (in comparison with the modern cultivar , Agria), was the latest to mature regardless of irrigation. The possible reason for this observation is that Taewa is not bred for early maturity comparable to modern cultivars. Early flowering in Taewa is part of their survival strategy (for seed production of the next generation) developed during self- selection (Roskruge et al. 2010 ) . This was also observed in the glasshouse (see Chapter 3). Nevertheless, adequate water was essential for canopy development, whereas water stress encouraged deep rooting, as observed in Taewa . It has been reported that dry matter is associated with LAI (Jefferies et al., 1993b) and therefore reduction in leaf features by water deficit decreases production, whilst it increases assimilation to the roots as an adaptation strategy to water stress, as reported by Liu et al. (2006b). 4.3.1.4.2 Photosynthetic WUE and gaseous exchange of Taewa and modern potato The field experiment in 2009/ 2010 persistently found photosynthetic WUE and An being influenced by cultivars, irrigation and DAE, as also observed in the glasshouse (Chapter 3) and other studies (Ghosh et al., 2000; Vos et al., 1989a; Vos et al., 1987) . Contrary to the glasshouse and Ghosh?s findings (2000), the highest photosynthetic WUE and An in this study was on 48DAE, in both Taewa and modern cultivars. This photosynthetic WUE trend still reflected An and it declined with age (Ahmadi et al., 2010; Gh osh et al., 200 0) . The seasonal photosynthetic WUE and An increased up to day 48 before declining with time, regardless of irrigation and cultivars, with the lowest on day 21 (see Appendix 4.4.3) . This suggests that the period of tuberisation, the likely cause of high An (Moorby, 1970 ) , is not static at 21 DAE, as observed in the glasshouse and reported by Ghosh et al. (2000), but it ranges from three weeks to seven weeks from plant emergence. Moe Moe had an extended high est photosynthetic WUE under irrigation, apart from the highest photosynthetic WUE and An under rain- fed conditions. Despite this finding, the average photosynthetic WUE and An, for Moe M oe and Agria, were comparable and this was also found in Tutaekuri and Moonlight (Table 4.1.3) . The high photosynthetic WUE characteristics of Moe Moe under rain- fed and the increased An and low Ci with irrigation indicate that increased water stress, during a drought year, may steadily affect CHAPTER 4 Field experiment on potato, oca and pumpkin squash 97 gaseous exchange in modern cultivars, unlike that seen in Tutaekuri . This shows that the ability to adapt to low water supply, as observed in the glasshouse (see Chapter 3) and reported in old wheat cultivars (Ko? et al., 2003), exists in Taewa. Generally, these findings confirm that A n and photosynthetic WUE in potato are limited by water deficit (Ahmadi et al., 2010; Olesinski et al., 1989) . Schapendonk et al. (1989) reported potato genotypic variation in An under well watered and limited water. However, the response to water deficit was primary regulated by stomatal closure followed by mesophyllic activity when water stress was severe, as also observed in most C3 plants (Flexas et al., 2002) . The Ci for rain- fed treatment in this study increased, thus signifying severe water stress to have fully induced An and photosynthetic WUE reduction. This is factual, because Ci is greatly affected by mesophyllic activity (Schapendonk et al., 1989) and it is inversely related to An ( Morison, 1998) . However, the results of this study differs from Olensinski et al. (1989), who found that Ci was not affected by water deficit and this study also disagree with Liu?s (2006a) report that photosynthetic WUE was higher under deficit irrigation than full irrigation. These results do not support suggestions that photosynthetic WUE is enhanced with restricted water use, possibly because A n for rain- fed decreased, while gs and T remained in the same range with the irrigated potato, which is contrary to other studies (Ahmadi et al., 2010; Liu et al., 2006a) . 4.3.1.4.3 Leaf water potential of Taewa and modern potato cultivars Water stress increased leaf water potential . However, the leaf water potential results did not demonstrate genotypic variability on leaf water potential, as reported in the Andean region between water regimes (Schafleitner et al., 2007) . The finding on leaf water potential confirms that potato leaf water potential is not as sensitive as gaseous exchange to water stress and hence it was not a very reliable indicator for cultivar tolerance to water stress, in 2009/ 2010 as formerly observed by Olesinski et al. ( 1989) . The result suggested that leaf water potential was very reliable indicator of water stress between water regimes, rather than potato cultivars. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 98 4.3.1.4.4 Dry matter partitioning and tuber yield of Taewa and modern potato The results of the dry matter partitioning confirm that old cultivars translocate more dry matter to their leaves, stems and roots , whilst modern cultivars optimise partitioning to the harvested products (Ziska et al., 2007). G enotypic variation in dry matter partitioning has been reported in four potato cultivars (Shepody, Frodo, Darius and Pentland Dell) by Geremew et al. (2007) and this has also been confirmed within Taewa and modern potato in this study. The substantial above- ground biomass and number of tubers per plant were responsible for the reduction of mean tuber weight and HI in Taewa. As the number of tubers per plant continued to increase in Tutaekuri, the mean tuber weight and HI deteriorated. This corresponds to Geremew?s (200 7) observation that the cultivar with the highest above- ground biomass (Shepody) ha s least translocation to tuber. I t can be proposed that the large sink in Taewa affect s tuber yields, due to diverse translocation of water and it assimilates at the expense of large tubers. However, these findings are unlike other studies (Jefferies et al., 1993 b; Geremew et al., 2007) , because it suggests that total dry matter production does not differ between cultivars ( Taewa and modern cultivars), but instead they only differ on how each cultivar allocates assimilates to each component. Consequently, cultivars that priotise translocation of assimilates to tubers have high tuber yield. The tuber yield results of this experiment substantiate and broaden other observations that irrigation improves potato yields (Erdem et al., 2006) and also that there are potato genotypic differences in water use (Steyn et al., 1998; Trebejo et al., 1990; Wolfe et al., 1983) . The results clearly show that total and marketable tuber yields are strongly influenced by irrigation in both Taewa and modern potato cultivars, but not in Tutaekuri. Potato yields increased linearly with irrigation , depending on genotypes and the highest increase was found in modern potatoes. Evidently , the response to irrigation is high in cultivars that are very sensitive ( or not tolerant) to water stress, which are predominantly modern cultivars. I nterestingly; it is supported by the high reduction of modern potato cultivars with a mild water stress, as compared to Taewa. This congruently supports Trebejo?s (1990) findings that cultivars which perform well under adequate water may not do well under water stress, unless the cultivar is stable to both a stressed and non- stressed environment, as observed with Moe M oe in this study. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 99 Moe Moe (Taewa ) is notable because it competitively produced equal tuber yields to modern cultivars. Moe Moe yield was also more than the average potato yield of 50.2 t ha- 1 in New Zealand . It is also above the world potato average yields, which range from 10.8 to 41.2 t ha - 1 (FAO, 2009) . The performance of Moe M oe dispels claims which generalise that Taewa cultivars are 50% poorer in their yields than modern potato (Harris et al., 1999) . It also indicates the possibility of achieving high yields in some Taewa cultivars, if water is managed correctly. Moe Moe showed a good yield, regardless of its many branches, relative to modern cultivars. On the other hand, irrigation outstandingly failed to improve the tuber yield in one Taewa cultivar ( Tutaekuri ) . Tutaekuri did not respond to irrigation like other cultivars, possibly due to differences in their sub- species and low HI . Tutaekuri is Solanum tuberosum ssp. andigena, whilst the other cultivars are Solanum tuberosum ssp. tuberosum. It is probable that a combination of irrigation with growth regulators, which have been reported to induce tuberisation in S. tuberosum ssp. andigena (Kumar et al., 1973, 1974) , could manoeuvre Tutaekuri to respond to irri gation, in a similar manner to other potato cultivars. Irrigation enhances potato yields differently, through the modification of mean tuber weight and number of tubers per plant, depending on the cultivar ( Belanger et al., 2002; Walworth et al., 2002) . According to this study, irrigation almost doubled the mean tuber weight in all the high yielding potato cultivars (Agria, Moonlight and Moe M oe) . H owever, the adjustment in Moe M oe was accompanied by a modification of the number of tubers per plant, whi ch were fewer than those under rain- fed condition. Consequently, total and marketable tuber yields between Agria, Moonlight and Moe M oe were the same, regardless of the differences observed in the number of tubers and mean tuber weight. Moe M oe managed to compete with the modern cultivars (Agria and Moonlight) in achieving high yields , due to an intermediate number of tubers and mean tuber weight. The increase in mean tuber weight confirms other findings by B?langer et al. ( 2002) , Ferreira et al. ( 2007) and Yuan et al. ( 2003), whilst a decrease in the number of tubers with irrigation is contrary to Belanger et al. (2002) and Yuan et al. ( 2003) , who reported an increase in tuber numbers per plant with irrigation. The substantial vegetative growth and high number of tubers per plant were responsible for the reduction of total and marketable yields in Taewa (Roskruge et al., 2010) . The CHAPTER 4 Field experiment on potato, oca and pumpkin squash 100 harvest index for Moe M oe and Tutaekuri was greatly affected by the large amount of vegetative growth. However, the increased number of tubers per plant in Tutaekuri increasingly deteriorated its tuber yield performance. These two traits increased the area for assimilates partitioning, at the expense of mean tuber weight improvement. Consequently, mean tuber weight was indifferent with irrigation in Tutaekuri , whilst Moe Moe increased mean tuber weight with irrigation and this instigated low total and marketable tuber yields in Tutaekuri . The yield component results depicts that the high number of tubers per plant heavily reduced the mean tuber weight and HI traits in the potato cultivars. This shows that Tutaekuri (as an old cultivar ) has low yields, because it allocates more water and assimilates, in order to sustain vegetative growth and more yield components, at the expense of large tubers, as reported in wheat ( Siddique et al., 1990a ) , soyabean (Frederick et al., 1991) and oat (Ziska et al., 2007). Conversely, a high vegetative biomass will have an advantage over a modern cultivar, in response to the rise in CO 2 that will be caused by climate change, as observed in oats (Ziska et al., 2007) . 4.3.1.4.5 Water use efficiency Moe M oe, a Taewa cultivar, had less or equal WUE to modern potato, whilst out performing Agria under water deficit conditions. As usual, the WUE for all cultivars was high under rain- fed (Zoebl, 2006) . Moe M oe competed with modern potato cultivars in WUE and tuber yield, due to its tolerance to both a stressed and non- stressed water environment. This confirms that Moe M oe has a comparable capacity in tuber yield and WUE to modern cultivars, as observed in the glasshouse (see Chapter 3). This study confirms that WUE in potato is affected by genotype and agronomical water management practices (Bowen, 2003; Trebejo et al., 1990). It is also notable that potato WUE for this study is within the global average, ( except for Tutaekuri ) which ranges from 6.2 kg m - 3 to 11.6 kg m - 3 (FAO, 2009 ) . Moe M oe had lower WUE under irrigation compared to Moonlight and Agria . The difference in WUE, b etween WUE in Moe Moe and modern potato under irrigation, is a result of late maturity in Moe M oe. Late maturity increased potential evapotranspiration, thus resulting in lower WUE in Moe Moe than modern potato. However, the WUE for Taewa under irrigation were still above the WUE of major world crops, such as rice, wheat and maize presented in literature review (Chapter 2) . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 101 This observation suggests that Taewa is more efficient under water stress compared to modern cultivars, which become more efficient when adequate water is available. Notably, low HI , an increased number of tubers per plant and a major disparity in appropriate agricultural husbandry practices, contribute to low yields and WUE in Taewa, in New Zealand . Apparently, appropriate water management will improve the total production of Moe Moe, unlike the case of Tutaekuri. 4.3.1.4.6 Specific gravity and tuber dry matter content Taewa had the highest SG and DM compared to modern cultivars, thus indicating great genotypic differences in tuber quality. Such DM and SG differences have been reported in several studies ( Wer ner et al., 1998; B?langer et al., 2002; Singh et al., 2008) . However, the SG range in Taewa (especially Tutaekuri ) is above the normal SG range of 1.055 to 1.0950 (Kellock et al., 2004) . Similar results (SG as high as 1.12 in potato) were reported by Verma et al., (1971) . Taewa results on SG and DM substantiate Singh ?s (2008) findings that also reported a high SG and DM in Moe Moe and Tutaekuri, compared to the modern cultivar , Nadine , apart from confirming the glasshouse results presented in Chapter 3. It is probably that heredity and the long growing cycle for Taewa enhances the accumulation of DM , which results in high SG. Wer ner et al. (1998) reported that SG increases with a long growing season. However, t he study did not affirm reports on the effect of environmental manipulation on SG and DM ( Killick et al., 1974; Kellock et al., 2004). S oil moisture hardly affected SG , as also reported in Russet Burbank and Shepody ?s potato cultivars (B?langer et al., 2002) . It is likely that the soil moisture modification was within the crop water requirement range for potat o and hence, it could not influence SG and DM. 4.3.1.4.7 Total sugars Moonlight had the highest total sugars followed by Agria, compared to Taewa. The concentration of sugars and DM in potato are usual benchmarks for processing potato quality assessment ( Marquez et al., 1986). High sugars badly affect colouring in potato fries (Marquez et al., 1986; Kumar et al., 2004), whereas high DM increases productivity of the processed product and the amount of oil used in chips ( Kellock et al., 2004). This finding suggests that Taewa can produce more processed products with less oil, compared to modern potato cultivars. Maori people might have wanted to grow Taewa because of its high solid and mealiness texture that easily meets their food and CHAPTER 4 Field experiment on potato, oca and pumpkin squash 102 cooking satisfaction (Singh et al., 2008 ) . In addition, Maori people believe that Taewa has nutritional attributes which can control particular health problems (McFarlane, 2007) . 4.3.1.5 Conclusion The results of this research indicates that irrigation and cultivars influence potato tuber yield and yield components. Modern cultivars had the least number of tubers per plant and the highest mean tuber weight, whilst the Taewa variety, Tutaekuri had the highest number of tubers per plant and the least mean tuber weight. Moe M oe was intermediate in both traits. The total and marketable tuber yields of Agria, Moonlight and Moe M oe increased with irrigation under both environments. Moe M oe?s yield was similar to modern cultivars but Tutaekuri was different . It can be concluded that some Taewa cultivars have comparable tuber yield and WUE to modern cultivars. Nevertheless, their increased vegetative growth, the higher number of tubers and inappropriate agricultural husbandry practices, contribute to low yields. Irrigation is recommended for Taewa and the best cultivars need to be used, due to genotypic influences (e.g. subspecies): Moe M oe can be irrigated in the expectation of high tuber yields. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 103 SECTION 4.3.2 OCA CULTIVARS? RESPONSE TO IRRIGATION AND RAIN-FED CONDITIONS 4.3.2.1 Introduction Oca ( Oxalis tuberosa Mol.) is one of the important Andean tuber crops grown in New Zealand and it is commonly known as New Zealand yam (Sangketkit et al., 2000). Oca has been commercialised in New Zealand, Mexico, Australia, France, Great Britain and Peru (Bormejo et al., 1994; Collins, 1993 and Flores et al., 2002, 2003) . Its use is generally restricted by its low yields, both in New Zealand (Ross, 1999 ) and in the Andean region (Bormejo et al., 1994; Sperling et al., 1990) . The low attainable yield in oca is a consequence of insufficient research and published agronomic work, despite its economic potential. The information available in New Zealand is rel ated to its genetic characterisation (Martin et al., 1999 ; 2005) ; storage and processing (Flores et al., 2002) ; and utilisation and biochemistry (Dubios , 2007) . F armers tend to manage water and other resources in oca crops by trial and error ( Pers. Comm. Osborne, 2009; Martin et al., 1999) . The literature shows that other root and tuber crops yields (such as potato) are strongly influenced by water availability and genotypes (Belanger et al., 2002; Walworth et al., 2002) . Oca f armers in New Zealand require scientific information on how to optimise their profits through cultivar selection and management of inputs, such as irrigation. Nevertheless, there have been very few studies o f oca and in particular their response to irrigation. This study investigated the effects of irrigation on tuber yield, tuber development and WUE of two oca cultivars. 4.3.2.2 Materials and Methods All details of the oca experiment materials and methods are presented in the general methodology section 4.2 above. This chapter section presents the results on plant physiological and morphological characteristics, yield and WUE for oca. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 104 4.3.2.3 Results 4.3.2.3.1 Crop water use and soil moisture content The growing season for oca was 224 days with a seasonal potential crop water requirement of 678 mm. P recipitation supplied 77% of the potential water requirement (Fig. 4.2.1). Irrigation added 200 mm, to meet at least 100% of the crop ?s water requirement in the irrigated treatment (Fig. 4.2.2). The crop water use for rain- fed was 75% of the irrigated crop (Table 4.2.2). Irrigation reduced the soil moisture deficit experienced between February and April, when precipitation was small (Fig . 4.2.1b, Appendix 4.4.2). This was evidenced by significant volumetric soil moisture content (%) variation s between water regimes and measured dates (P <0.0001). Soil moisture in the rain- fed treatment was lower and it ranged between 15 - 20% , whilst irrigated treatments ranged between 20- 35% (Fig. 4.2.1) . Figure 4.2.1 (a) Rainfall distribution , irrigation, maximum and minimum temperature during the growing season, 2009/ 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 105 Figure 4.2.1 (b) S oil moisture content change during the growing season. Error bars represents ?SEM . Figure 4.2.2 Potential and Actual c rop water use (mm) under rain- fed and full irrigation for oca, 2009/ 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 106 4.3.2.3.2. Photosynthetic water use efficiency and gaseous exchange Net photosynthesis (A n, ?mol CO 2 m 2 s- 1 ) ; photosynthetic WUE ( ?mol CO 2 /m molH 2 O); and VPD (mb) were significantly influenced by the water regime (P<0.05, P<0.05, P<0.01) (Table 4.2.1). Oca cultivars had no significant effect on gaseous exchange (P>0.05). Net photosynthesis , T, g s , photosynthetic WUE, Ci and VPD significantly differed between DAE (P<0.001, P<0.01, P<01, P<0.0001, P<0.01, P<0.0001) (Table 4.2.1) . The irrigation treatment had the highest An and photosynthetic WUE and lowest VPD, whilst the rain- fed regime had low An and photosynthetic WUE and highest VPD and Ci. Net photosynthesis and photosynthetic WUE increased from Day 21 to Day 48, before it decreased at Day 64 and increased again on Day 90, before decreasing again on Day 157. The trend for gaseous exchange in oca shows net photosynthesis and photosynthetic WUE decrease on Day 64 and 157 following high VPD and low leaf stomata conductance (g s ) , under rain- fed conditions. The relationship between photosynthetic WUE and gaseous exchange variables was explored with all data combined and using simple correlation. It was found that photosynthetic WUE negatively correlated with T (r = - 0.58, P<0.0001); Ci (r = - 0.40, P<0.01); VPD (r = - 0.59, P<0.0001 ); and positively correlated with An (r = 0.73, P<0.0001) and g s (r = 0.34, P<0.01). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 107 Table 4.2.1 Photosynthetic water use efficiency and gaseous exchange in two oca cultivars under irrigation and rain - fed conditions CHAPTER 4 Field experiment on potato, oca and pumpkin squash 108 4.3.2.3.3 Tuber growth and development Tuber fresh biomass of oca varied between the sampling dates (P <0.0001 , Fig . 4.2.3). There was no tuber formation prior to 100 days from planting. Tubers were initially observed as developing in the irrigated dark orange oca (4.8 g plant- 1 ) and s carlet oca (13.8 g plant- 1 ) , 132 days after planting ( DAP ) (22 nd March) (Fig .4.2.3b). The tuber biomass slightly increased in the irrigated dark orange and scarlet oca to 68.6 g and 65.4 g per plant, compared to the rain- fed dark orange and scarlet oca, which had only developed up to 26.6 g and 52.7 g per plant, after 154 DAP (13 th April), respectively. The tuber biomass for rain- fed ( on this date) was 38.8% and 80.6% of irrigated dark orange and scarlet oca, respectively. By 3 rd May, the tuber biomass had increased in the irrigated dark orange and scarlet oca to 502 g and 521 g per plant, whilst the rain- fed dark orange and scarlet oca had increased to 355.5 g and 470.4 g per plant. The rain- fed dark orange and scarlet oca tubers were still at a lower level (compared to the irrigated plants) at 70.8 % and 90.3% , respectively. Final tuber fresh biomass for irrigated dark orange and scarlet oca was 608.1 g and 669.4 g per plant, whilst rain- fed dark orange and scarlet oca was 439.1 g and 556.1 g per plant, at harvest (Fig . 4.2.3). The total tuber biomass per plant, for rain- fed, was between 72% and 83% of the irrigated tubers at harvesting. The tuber growth rate increased as the days? le ngth shortened up to May and then it declined in June (Fig .4.2.3a). The highest tuber growth rate , which ranged from 14.45 - 15.2 g per day and 10.96- 13.92 g per day in irrigated and rain- fed dark orange and s carlet, respectively , was observed in May (Fig .4.2.3a). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 109 Figure 4.2.3 (a) Oca tuber growth rate (g/day) and (b) tuber biomass (g/plant) at different sampling dates on fresh weight basis. Error Bar is ?SEM CHAPTER 4 Field experiment on potato, oca and pumpkin squash 110 4.3.2.3.4 Total and marketable tuber yield, yield components and WUE Irrigation had a significant effect on total tuber yield and the number of tubers per plant (P <0.05) , but it had no effect on average tuber weight (P >0.05). Cultivar influenced the number of tubers per plant (P <0.05) (Table 4.2.2). The total tuber yield was strongly influenced by the number of tubers per plant, rather than the average tuber weight. Marketable tuber yield and marketable tuber yield components were not different between oca cultivars, but they were different between water regimes. Table 4.2.2 shows that the number of L - grade marketable tubers, L - grade marketable tuber yield and total marketable tuber yield were influenced by irrigation (P <0.01, P<0.01, P <0.05) , whereas medium grades (M - grades) were not influenced by irrigation (P>0.05) ( Table 4.2.2). The WUE evaluated, based on total tuber yield at harvest per volume of water used was not significantly influenced by irrigation or cultivar (P>0.05; Table 4 .2.2). The WUE ranged between 3.3- 3.7 ( k g ha- 1 m- 3 ) (Table 4.2.2) . 4.3.2.4 Discussion 4.3.2.4.1 Crop water use and soil moisture content The oca growing season in the Andean region is between 6 - 8 months with a water requirement of 400 - 70 0 mm (Arbizu et al., 1997; King, 1987) . The study found 678 mm as being the potential water requirement within 7.5 months. The result also indicates that oca water requirement is within the range of potato (500 - 700 mm) (Allen et al., 1998; Shock et al., 2007) . However, o ca water use might be more variable, due to weather variability within its extended crop life - cycle, in contrast to potato. This proposition is not in agreement with what Flores et al. (2003) once speculated that oca may require up to 2500 mm of water for production. I rrigation was important for this crop in order to maintain optimal soil moisture during growth and tuber development stages (Fig .4.2.1 a- b and Fig. 4.2.3 ). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 111 Table 4.2.2 Total yield, yield components and WUE for oca under irrigation and rain- fed conditions, 2009/ 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 112 4.3.2.4.2 Photosynthetic water use efficiency and gaseous exchange Water stress increases the leaf VPD resulting in limited photosynthesis in plants (Bunce, 2003, 2009) . The results confirmed that water stress ( under rain- fed) increased leaf VPD in oca, whilst irrigation reduced it. Consequently, photosynthetic WUE and A n were reduced under rain- fed with high VPD [ An= - 0.64 (VPD) + 25.2, r = 12.4, P<0.01] , compared to irrigated plots. This observation suggests that the high leaf VPD in the rain- fed treatment was caused by leaf water deficit and a reduced water supply to the roots of the oca (Monteith et al., 1986) . Irrigation closed the gap of moisture deficit between the leaf and the surrounding air, by supplying more water to the roots, regardless of cultivar. Judging from the leaf vapour pressure deficit and photosynthetic results, water deficit is one of the major limiting factor s for high photosynthetic WUE in oca. 4.3.2.4.3 Tuber formation and growth Oca tuber biomass and growth rate increased , as day length shortened, confirming that it is day- length reliant and that tubers develop as day length become shorter after the autumnal equinox (Arbizu et al., 1997; Martin et al., 2005) . In this case ( 22 nd March), the autumnal equinox day for the s outhern hemisphere is the time that the oca tuber starts forming in New Zealand. However, the effect of temperature on tuber formation needs to be thoroughly investigated, since short days are always accompanied by lower temperatures. This study also suggests that photo- period sensitivity restricts oca from being adapted in other parts of the world (Sperling et al., 1990; Martin et al., 2005) . Apart from the day- length effect, tuber set and growth was delayed in rain- fed, indicating the adverse effects of water stress on tuber setting and development, as also observed in photosynthesis above. A similar response to water stress has also been reported in potato (Shock et al., 2007) . This leads to the conclusion that optimal water is essential for oca tuber formation and development during the autumn period. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 113 4.3.2.4.4 Total tuber yield, marketable tuber yield and tuber yield components Irrigation enhances total and marketable tuber yield in oca, similarly to potato (Erdem et al., 2006; Ferreira et al., 2007) . O ca responded to irrigation primarily through an increase in tuber numbers per plant, thus resulting in increas ed total tuber yield (Table 4.2.3). The genotypic variation in tuber numbers has also been reported in potato. However, most potato cultivars are accompanied by average tuber weight variation under irrigation (B?langer et al., 2002 ) . In this study, irrigation enhanced total tubers per plant (depending on the cultivar) and it enhanced the number of premium marketable tubers, regardless of cultivar. The study shows that development of premium marketable tubers in oca production is more governed by adeq uate water than cultivar. The premium marketable tubers of oca were a result of the enhanced allocation of assimilates to tubers with adequate moisture . Irrigation almost doubled the marketable tuber yield through tuber enlargement. There is substantial evidence that irrigation modified the number of premium marketable tubers , as in potato ( Solanum tuberosum) (Ferreira et al., 2007; Shock et al., 2007 ) . Furthermore, irrigation enhanced photosynthetic WUE and A n. This substantiated the adverse response of oca to water stress and it verifies that oca total and marketable yields are well enhanced with optimal soil moisture. On the other hand, t he tuber yields obtained under rain- fed, in this study, wer e higher than those reported in the Andean region ( 3- 12 t ha - 1 ) (Bormejo et al., 1994) : but they were within those levels reported in New Zealand ( 12- 16 t ha - 1 ) (Martin et al., 1999). Total tuber yields under irrigation demonstrate the possibility of doubling the present oca yields in New Zealand and the Andean region if optimal water management is used (King, 1987 ) . The tuber yield increase with optimal water and nutrients, which have been thoroughly documented in relation to modern potatoes (Ferreira et al., 2007; Shock et al., 2007) , can be readily achieved in oca. However, o ca is not efficient in its water use and its crop water productivity is strongly affected by its long life of 224 days. This confirmed by its equal WUE between irrigation and non- irrigated treatments. The usual trend in potato and other crops is that highest WUE is in non- irrigated (Battilani et al., 2004; Zoebl, 2006) . The implication of this result is that water management in oca should be of great concern, because water can only be optimised CHAPTER 4 Field experiment on potato, oca and pumpkin squash 114 through correct phenology manipulation, or by using agronomic practices which will improve WUE but not selection of cultivars (Boutraa, 2010). 4.3.2.5 Conclusion The results of the study indicated an adverse reduction in photosynthetic water use efficiency; increased leaf vapour pressure deficit; and reduced tuber growth and development in rain- fed oca, compared to irrigated oca. Oca total yield and marketable yield improved under irrigation, regardless of crop cultivar. W UE was found to be strongly affected by the oca long lifecycle. It can be concluded that oca is short- day dependent and that tuber set, total yield and marketable yield , are highly enhanced with irrigation, which is similar to potato . However, WUE in oca is not efficient, as seen in potato. Its crop water productivity is strongly influenced by its high potential evapotranspitation, which is sustained from its long life cycle. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 115 SECTION 4.3.3 MODERN AND HERITAGE PUMPKIN SQUASH CULTIVARS? RESPONSE TO IRRIGATION AND RAIN-FED CONDITIONS.3 4.3.3.1 Introduction Kamokamo ( Cucurbita pepo Linn ) is a heritage pumpkin cultivar originally grown by the Maori people of New Zealand (McFarlane, 2007). Generally, it sells in a niche market, in contrast to Buttercup squash (Cucurbita maxima Duchesne ) , which is an important commodity crop exported to Japan and Korea (Hume, 1982; Perry et al., 1997) . However, there has been a resurgence of interest in Kamokamo , due to its cultural value and delicious flavor. M arket demand has also facilitated an increase in B uttercup squash production in New Zealand (Grant et al., 1989) , Tasmania and Korea, whilst Japan recorded a yield decrease (Morgan et al., 2003) . On the other hand, the Buttercup squash industry experiences fruit yield and fruit size fluctuations between seasons due to the pumpkin squash?s sensitivity to seasonal climate variability (Perry et al., 1997) . Pumpkin squash y ield and standard fruit size are strongly influenced by water availability and also by genotypic variability (Al - Omran et al., 2005; Ertek et al., 2004) . New Zealand farmers need to be able to manage pumpkin squash fruit quality and water conservation due to a projected water scarcity (IWM I, 2000 ) . Prudent use of water resources ( Hoekstra et al., 2007 ) and the correct pumpkin cultivars will help growers to meet yield and quality demands , which will maximize financial returns (Searle et al., 2003) within adverse climate variability (Perry et al., 1997) . However, there is scarce scientific information on the agronomic performance of pumpkin squash under different water environments in New Zealand. Th is field experiment was conducted, in order to measure fruit yield, WUE and fruit size distribution in B uttercup squash, compared to the heritage cultivar, Kamokamo , under irrigation and rain- fed conditions. 3 Section 4.3.3 is published as: Fandika, I.R Kemp, P.D., Millner, J.P and D. Horne (2011). Yield and water use efficiency in ( Cucurbita maxima Duchesne) Buttercup squash and ( Cucurbita pepo Linn) heritage pumpkin cultivar. Australian Journal of Crop Sciences, 5(6 ) :74 2 - 7 4 7 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 116 4.3.3.2 Materials and Methods All the details of the pumpkin squash experiment materials and methods are presented in the general methodology section ( 4.2) above. The following section presents the results on plant physiological and morphological characteristics, fruit yield and WUE for pumpkin squash. 4.3.3.3 Results 4.3.3.3.1 Crop water use and soil moisture content Figure 4.3.1 Potential and actural c rop water use (ET c ) (mm) under rain - fed and full irrigation for pumpkin squash, 2009/ 2010. The growing season for the pumpkin squash was from 9 th December, 2009 to 30 th March, 2010 (110 days) , which is equivalent to 3.7 months. The seasonal crop water requirement for the pumpkin squash was estimated at 442.1 mm (Fig. 4.3.1) . Precipitation supplied 232.8 mm, which was 53% of the estimated total water requirement. Irrigation added 175 mm, which met at least over 90% of the crop water requirement within the irrigated treatment. The rain- fed B uttercup and Kamokamo used 258.7 mm and 264 mm, whilst the supplementary irrigated crops used 407.6 mm and CHAPTER 4 Field experiment on potato, oca and pumpkin squash 117 413.2 mm, respectively. Irrigation was a requirement in January, February and March when precipitation was poorly distributed (Fig. 4.3.1, Fig.4.3.2 and Appendix 4.4.2). Figure 4.3.2 Volumetric soil Soil moisture measurements corresponding to periodical precipitation (mm) and irrigation (mm) , 2009/ 201 0. Error bar represents ?SEM. Volumetric soil moisture content (%) differed with water regime s and crop cultivars and between measurement dates (P<0.0001, P<0.05, P <0.0001), respectively (Fig. 4.3.2) . Soil moisture in rain - fed treatments ranged between 15 - 25% , whilst irrigated treatments ranged between 20 - 35% , except in February when soil moisture was depleted to less than 20%. Kamokamo extracted more water than Buttercup squash in both water regimes. 4.3.3.3.2 Pumpkin squash growth and yield components characteristics With or without irrigation, pumpkin squash cultivars differed in LAI at all four different sampling stages (P <0.0001; Table 4.3.1; Fig. 4.3.3). Kamokamo had a higher LAI and SLA , compared to Buttercup squash. The LAI increased from D ay 21 to D ay 80 ( from emergence) . Leaf area index was sporadically reduced by frost in the month of March, 2010. Buttercup f lowered earlier than Kamokamo (P <0.0001) , regardless of the water regime (P >0.05). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 118 The number of fruit per plant was unaffected by irrigation (P >0.05). The mean fruit weights were significantly higher in Kamokamo under a rain - fed regime (P <0.05) , but there was no difference within the irrigated treatments. The mean fruit size had more influence on fruit yield, compared to the number of fruit (Table 4.3.1; Plate 4.3.1). Figure 4.3.3 Change of LAI in Buttercup squash and Kamokamo during the growing season 4.3.3.3.3 Pumpkin squash fruit size distribution The fruit size distribution for large marketable fruits (L=1.4?2.5 kg) was significantly higher than other fruit size ranges (P <0.05; Fig. 4.3.4; Plate 4.3). The irrigated treatments had a higher percentage of fruit within this fruit size range (L=1.4 ? 2.5 kg) : the highest was seen in the irrigated Buttercup squash (82.9%). Kamokamo had more extra- large fruit and small non- marketable fruits than Buttercup squash, especially under rain- fed conditions (Plate 4.3) . CHAPTER 4 Field experiment on potato, oca and pumpkin squash 119 Plate 4 3 : A sample of pumpkin squash fruit size distribution under different water regimes per plot. 4.3.3.3.4 Pumpkin squash fruit yield and water use efficiency (kg ha-1m-3) With or without irrigation, the amount of dry vines plus leaves per hectare and total fruit yield varied in Buttercup squash and Kamokamo, respectively (P<0.0001, P<0.05; Table 4.3.1). Marketable fruit yield and HI did not differ between the two cultivars and their water regimes (P >0.05). Kamokamo prevailed over Buttercup squash in al l the above traits, except in HI. The high LAI did affect HI in Kamokamo. Although the water regimes did not affect the fruit yield, there were minor levels of water stress effects seen in the reduction of HI and fruit yield under the rain- fed conditions ( Table 4.3.1). Most of the non- marketable fruit was based on immaturity and low fruit weight (<1 kg) , rather than disease impairments. WUE , based on total fruit yield per total water used, was affected by both the water regime and the crop cultivars ( P<.05, P<0.01; T able 4.3.1). Kamokamo had a higher WUE than Buttercup squash. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 120 Table 4.3.1 Growth and fruit yield components characteristics, total and marketable fruit yield, H I and WUE for Buttercup squash and Kamokamo CHAPTER 4 Field experiment on potato, oca and pumpkin squash 121 4.3.3.4 Discussion It is claimed that p umpkin squash fruit yield increases with increasing water application and declines when water is in excess or limited (Al - Omran et al., 2005) . In this study , fruit yield failed to respond to irrigation, possibly due to rainfall that made the soil wet soon after irrigation. Consequently, the after irrigation rainfall spatially reduced fruit yield response to irrigation. In spite of this , irrigation influenced the standard fruit size for the export market , both in Buttercup squash and Kamokamo (Fig. 4.3.4). The results on standard fruit size in Fig. 4.3.4 indicate that, although irrigation may not be of significant importance for total fruit yield in a good year, it facilitates quality control for marketable fruit sizes , compared to rain - fed conditions (Fig. 4.3.4 & Plate 4.3.1). The results suggested that more flowers are sustained under irrigation than under rain- fed conditions. The fewer flowers maintained under rain- fed conditions translated into larger fruit than for irrigated conditions (Plate 4.3.1). There has not been a previous report on irrigation influence on pumpkin fruit size in New Zealand. However, lots have been reported by Fletcher et al. (2000) on how diseases reduce fruit number and size in B uttercup squash. In this study , irrigation played an important role in the reduction of pumpkin squash fruit variability. Perry et al., (1997) reiterated that fruit size fluctuations are a great problem in pumpkin squash industry where specific fruit size is a requirement. I rrigation, in order to manipulat e specific market fruit size , needs to be well modelled, as previously undertaken with plant densit y studies (Lima et al., 2003) . Total yields and marketable yields were slightly greater than those obtained by the majority of growers in New Zealand (Buwalda et al., 1987) , Tasmania, Australia (Morgan et al., 2003) and other parts of the world. The cultivar had more influence on the pumpkin squash yield, when the environment was not limiting, as also reported by Morgan et al. ( 2003) . In this case, the results indicate that Kamokamo has a high fruit yield and WUE potential, compared to Buttercup squash. It was also observed that the high yield in Kamokamo was due to its ability to produce fruits of larger size than Buttercup squash. The high yield in Kamokamo, a Cucurbita pepo species contradicts St. Rolbiecki et al. (2000) , who reported that Cucurbita maxima cultivars have high production efficiency, compared to the Cucurbita pepo species of pumpkin squash. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 122 Figure 4.3.4 Number of size distribution (%) for irrigated and rain- fed Buttercup squash and Kamokamo: NM is non- marketable, S is small, M is medium, L is large and XL is extra large marketable fruit sizes. Error Bar represents LSD 0.05 W ater use efficiency vary with crop types, management system, year or location (Nielsen et al., 2006) . In this study , Kamokamo (18.9 ? 26 kg ha - 1 m- 3 ) had a higher WUE than Buttercup (13.4 ? 18.6 kg ha - 1 m- 3 ). Irrigation decreased WUE , as also reported in potato (Battilani et al., 2004) and other crops. Nevertheless, the value for WUE in Kamokamo and Buttercup were above those reported among st the world?s major crops (wheat, rice, maize, oat, potato, grain legume and forage grass) (FAO, 2009; Siddique, et al., 2001) . The WUE findings project that pumpkin squash has a high ability to transform water into more carbon than most of the world?s major crops , including forage grass and potato. The possible reason for the high WUE in pumpkin squash is its high fruit yield within a low potential evapotranspiration, which is a result of a short growing season, compared to other major world crops and forage crops. In this study , the old cultivar, Kamokamo, had more shoot biomass, fruit yield and WUE but it had low HI , compared to the modern cultivar, Buttercup squash. The high foliage and low HI supports Siddique et al. ( 199 0a ) , who reported that modern crops CHAPTER 4 Field experiment on potato, oca and pumpkin squash 123 have enhanced HI , whilst old cultivars have more foliage. The reason is that modern cultivars are bred for high HI. However, the improvement of HI in Buttercup squash did not increase fruit yield and WUE above Kamokamo, as reported in grain crops, where WUE was improved with the enhancement of HI in modern crops (Siddique et al., 1990a ) . Primarily, fresh biomass is essential for determining production in cucurbit species, rather than HI (Loy, 2004) . This indicates that Kamokamo, a heritage cultivar of New Zealand, has more potential for yield and WUE traits , than the modern Buttercup cultivar ?and this potential need s to be fully exploited in the near future, within the pumpkin squash industry. 4.3.3.5 Conclusion The results indicate that irrigation improves the development of standard marketable fruit sizes in pumpkin squash but not the total marketable fruit yield . The cultivars differed in total fruit yield and WUE . Increased water supply decreased WUE. The cultivar with the greatest WUE was that with greatest yield. Total fruit yields and WUE components , were highest in Kamokamo, which was a result of a high mean fruit weight, LAI and water extraction, respectively. On the other hand, both Kamokamo and Buttercup squash exceeded the WUE observed in major world crops. Pumpkin squash is a crop with high water productivity traits. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 124 SECTION 4.3.4 COMPARISON OF KEY WATER USE EFFICIENCY INDICATORS FOR HERITAGE AND MODERN POTATO, PUMPKIN SQUASH AND OCA CULTIVARS 4.3.4.1 Introduction Optimis ation of yield and water use is of great concern in both modern and heritage crop production systems. Sections 4.3.1 ? 4.3.3 confirm the importance of irrigation to yield improvements in some heritage and modern crop cultivars. Growers of these crops need k nowledge of irrigation water use efficiency, economic water productivity and water footprints, in order to successfully grow these crops and to help them optimise resource use and maximise profitability ( Barker et al., 2003; Hoekstra et al., 2007) . These concepts are becoming more important and they may influence future market access and water conservation targets in heritage and modern crop cultivars (MAF, 2004a) . Irrigation water use efficiency, economic water productivity and water footprints associated with the growing of arable crops have not been examined amongst modern and heritage crop cultivars in New Zealand. The following hypothetical question s were asked: What is the impact of additional water input on the studied heritage crop cultivars compared to modern crop cultivars, in relation to yield or cash per water used? How much water is required to produce a tonne of specific heritage crop cultivars, compared to modern crop cultivars? In order to answer these questions, this section analyses irrigation water use efficiency (IWUE); water stress index ; economic water productivity (EWP); and water footprints (WF), when growing heritage and modern potato, pumpkin squash and oca cultivars under rain- fed or irrigation in New Zealand. The section initially presents a summary of the crop water use and yield results from preceding sections, followed by water productivity results. The summary integrates all the studied crops to easily assess how the water productivity indicators (IW UE, EWP and WF), when growing heritage and modern potato, oca and pumpkin squash, can vary with crop management and cultivars. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 125 4.3.4.2 Materials and Methods The details of the field experimental design, crop and irrigation management are presented in S ection 4.2. This section will only present the results on key water use efficiency indicators. 4.3.4.3 Results 4.3.4.3.1 Crop water use and total yield summary Consumptive water use (m 3 ha- 1 ) was greatest in oca and lowest in pumpkin squash, whilst potatoes were intermediate, despite variation within cultivars (Appendix 4.4.1) . The modern and heritage crops differed in their relationship between their maximum water requirement and actual evapotranspiration, thus crop coefficient (k c ) and maturity (Fig. 4.4.1). Taewa and Kamokamo used more water compared to modern cultivars ( Table 4.4.2, Appendix 4.4.2) . Green water was approximately 62%, 65 %, 58% and 70% of consumptive water use , under irrigated modern potato, Taewa, pumpkin squash and oca, respectively. The dilution requirement (i.e the grey water) for the applied N in potato or oca and pumpkin squash had the equivalency of 425 m 3 ha- 1 and 398 m 3 ha- 1 , respectively (Table 4.4.2). Grey water increased in potato and oca compared to pumpkin squash, due to an increasing N rate. Total yields amongst the eight cultivars were strongly influenced by water regime and cultivars, with yields showing a continuous increase, from rain- fed to irrigated condition, except in the case of Tutaekuri (P<0.0001), which ranged from 23.2 t ha - 1 to 78.0 t ha - 1 in irrigated fields and from 16.7 t ha - 1 to 67.7 t ha - 1 in rain- fed treatments. The greatest total yields were in Kamokamo, whilst the least total yields were observed in dark orange oca, under both water regimes (P<0.0001). The total yields for Kamokamo were significantly different from Agria, Buttercup squash, Moe Moe and Moonlight, which were not different between themselves, but different to Tuta ekuri, scarlet oca and dark orange oca (P<0.0001 ). The total yield results demonstrated that scarlet and dark orange oca and Tutaekuri were the least in yields, out of the eight crop cultivars (Table 4.4.2). Partitioning to the harvested part was clearly d emonstrated by the highest HI in Agria, followed by Moonlight and Moe Moe. The lowest HI was in oca cultivars, whilst pumpkin squash and Tutaekuri were intermediate. Heritage crop CHAPTER 4 Field experiment on potato, oca and pumpkin squash 126 cultivars had extreme and relatively high vegetative biomass, compared to mo st modern cultivars in all the crops studied (Table 4.4.2) . Figure 4.4.1 Crop coeficients and overlapping maturity period for modern potato, Taewa, oca and pumpkin squash, 2009/ 2010 4.3.4.3.2 Irrigation water use efficiency and water stress index Irrigation water use efficiency (IWUE ), geometrical mean (GM), drought intensity index (DII) and yield percentage reduction (PR) with water stress were significantly different between potato, pumpkin squash and oca cultivars, (P<0.05, P<0.0001, P<0.01, P<0.05), respectively (Table 4.4.1) . The DII was significantly greater for potato than for pumpkin squash cultivars. However, all crop cultivars were below the severe water stress cut- off point of 0.7. The GM of the total yield was greatest in Kamokamo and least in dark orange oca (P<0.0001). The y ield percentage reduction showed that total yield for Agria, Moonlight and dark orange oca were heavily affected by water stress, whilst Tutaeku ri yield was not affected by water stress. I rrigation WUE was highest in plants which were more sensitive to water stress (Table 4.4.1). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 127 Potato cultivars (except Tutaekuri) as measured by IWUE significantly responded to irrigation application (P<0.05; P<0.01; P<0.05). Moonlight was the most responsive potato cultivar to irrigation, with a total tuber yield increase of 9.8 kg ha - 1 m- 3 , followed by Agria (9.4 kg ha - 1 m- 3 ) and Moe Moe (5.5 kg ha - 1 m- 3 ). Tutaekuri decreased total tuber yield by 1.3 kg ha - 1 m- 3 with irrigation. The two pumpkin squash and two oca cultivars were almost intermediate. Kamokamo was the most responsive pumpkin squash cultivar, with a yield increase of 5.2 kg ha - 1 m- 3 , compared to Buttercup squash (3.7 kg ha - 1 m- 3 ), as was d ark orange oca (3.9 kg ha - 1 m- 3 ) to s carlet oca cultivar (2.4 kg ha- 1 m- 3 ). The results indicate that there is a linear relationship between total yield and crop water use in all eight crop cultivars (Table 4.4.1). Table 4.4.1 Irrigatio n Water Use Efficiency ( IWUE ) , Drought Intensity Index (DII) , G eometrical Yield Mean (GM) and Percentage R eduction (PR %) of yield in heritage and modern crops cultivars, 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 128 4.3.4.3.3 Water footprint of growing heritage and modern crop cultivars 4.3.4.3.3 .1 Blue, green and grey water footprint on total yield basis The green, blue and grey water footprint ( WF ) components varied with both crop cultivars and water regimes (P<0.0001) , as presented in Tables 4.4.2. The consumptive WF (blue plus green WF or pure green WF) ranges were high in the irrigated field and low in the rain- fed field (Table 4.4.2). The average total consumptive WF increases with irrigation, from 140 to 155 (m 3 tonne- 1 ). The total consumptive WF increased with irrigation in Moe M oe (9%), Tutaekuri (49%), Buttercup squash (34%) , Kamokamo (34%) and scarlet oca (9%) whilst decreasing the total consumptive WF in Agria (2%), Moonlight (0%) and d ark orange oca (5% ) (Table 4.4.2). The cultivars with high IWUE had low WF under irrigated conditions, compared to rain - fed condition and vice versa (Table 4.4.1). In the irrigated crops, the blue WF comprised 27 - 39% , whilst the grey WF made up to 6 - 9% of the total WF . The high yielding crops, per water unit, equal ed low WF. All WF components were largest in d ark orange oca and smallest in pumpk in squash, Kamokamo (Table 4.4.2) . 4.3.4.3.3.2 Total water footprint of heritage and modern crop production Total WF of growing potato, oca and pumpkin squash on total yield varied with crop cultivars (P<0.0001) and it ranged from 58 to 310 m3 tonne- 1 under irrigation and from 46 to 335 m3 tonne- 1 under rain- fed (Table 4.4.2). D ark orange oca had the largest average total WF , whilst pumpkin squash, Kamokamo, had the least (P<0.0001) (Figure 4.4.1; Table 4.4.2). The pumpkin squash cultivars and Moonlight were not significantly different on total WF , but they were different to Moe M oe, Agria, Tutaekuri and oca cultivars. Tutaekuri had the greatest total WF among st the potato cultivars, although it was significantly lower than the oca cultivars (P<0.0001). Regardless of the crop water use increase with irrigation, the total WF between irrigation and rain - fed regimes were not statistically different (P>0.05). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 129 Table 4.4.2 Consumptive and total water footprint of growing potato, oca and pumpkin squash crop cultivars on total yield (m 3 ton.- 1 ) in New Zealand, 2009/ 2010 CHAPTER 4 Field experiment on potato, oca and pumpkin squash 130 4.3.4.3.4 Economic water productivity for modern and heritage crops Economic water productivity (EWP) , on a marketable yield basis , significantly differed between crop cultivars and water regimes (P<0.0001; Table 4.4.3). The rain- fed Agria, Moe M oe, Tutaekuri, Kam okamo and Buttercup squash had a greater water productive value than the irrigation treatments, whilst Moonlight had a great er EWP value under irrigation (Table 4.4.3). The o ca cultivars? economic water productive value was similar between the two water regimes. The average EWP , per variety, shows that pumpkin squash, Kamokamo, had the greatest value per water unit under both water regimes (a pproximately 42.30 NZ$/m 3 ) and oca, especially d ark orange oca, had the lowest E WP (a pproximately 4.40 NZ$/m 3 ). Amongst the four potato cultivars, Moe M oe displayed a high EWP ( approximately 33.50 NZ$/m 3 ), which was not significantly different from Ebisu (Buttercup squash) , but it was significantly greater than other potato/oca cultivars and significantly lower than Kamokamo (P <0.0001) (Table 4.4.3). The two heritage cultivars, Kamokamo (pumpkin squash) and Moe M oe (potatoes) , effectively outweighed the modern cultivars (Buttercup squash, Moonlight, Agria) in EWP (Table 4.4.3). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 131 Table 4.4.3 Economic water productivity (NZ$) on marketable yield basis in heritage and modern crop cultivars under irrigation and rain- fed conditions CHAPTER 4 Field experiment on potato, oca and pumpkin squash 132 4.3.4.4 Discussion 4.3.4.4.1 Crop water use and total yield production M odern and heritage crops differ in their relationship between their maximum water requirement and actual evapotranspiration, thus crop coefficient (k c ) , in addition to maturity. Figure 4.4.1 shows how the crop coefficient (or growing stages) overlapped during the growing season. The actual implementation of irrigation may result in over- irrigating pumpkin squash in order to meet the water requirements of other crops. It was discovered that differences in growth stages and maturity, between crops and within potato cultivars (Taewa and modern potato) , created disparities in their water requirement s (Allen et al., 1998) . Taewa and oca have an extended crop development time and mid- stages and ( as a result) these are the stages that are generally affected by drought according to volumetric soil moisture, whereas their later stage is frequently affected by frost, especially oca. The volumetric soil moisture indicates that the fully irrigated treatment maintained the soil water content within the available water level, which is regarded as critical for maximum yield in many crops (Ferreira et al., 2007). In contrast, the rain- fed treatment did not fully balance the water required by the plants and as a result the plants extracted more stored water from the soil profile. The heritage cultivars ( Kamokamo and Moe M oe) managed to extract more water than their counterparts under water deficit conditions. The majority of the heritage crop cultivars used more water than the modern cultivars. It is probable that the longer growth cycle in heritage crop cultivars (Kamokamo, Taewa and oca) resulted in them using more water than the modern cultivars. The crop evapotranspiration results provide a benchmark for the water requirement s of heritage and modern crop cultivars of potato, oca and pumpkin squash in New Zealand (Appendix 4.4.1). Perfomance of Kamokamo and Moe M oe signified their capacity to survive limited water conditions. The increases in yield components, with the use of irrigation, measured in this study, broaden previous observations that irrigation improves potato yields (Ferreira et al., 2007) and pumpkin squash yields (Al - Omran et al., 2005; Morgan et al., 2003) . However, the effect of irrigation on oca yields has not been reported. In t his study the rain- fed oca yields were greater than those reported in the Andean region (Bormejo et CHAPTER 4 Field experiment on potato, oca and pumpkin squash 133 al., 1994) and yet, the yield were within those reported in New Zealand (Martin et al., 1999), while the irrigated oca yields were above normal average yields (King, 1987) . The overall analysis shows that, amongst the crop cultivars studied, other heritage cultivars (Kamokamo and Moe Moe) produced relatively more than expected, when compared to modern crop cultivars (Table 4.4.2). 4.3.4.4.2 Irrigation water use efficiency The total and marketable yields of all the crop cultivars studied were responsive to water supply, except for Tutaekuri. W ater stress reduced the total yields of rain- fed crops to 34%, 31%, 24 % , 13%, 12%, 27%, 17 % of irrigated Agria, Moonlight, Moe M oe, Buttercup squash , Kamokamo, Dark O range and Scarlet oca, respectively. Comparatively, the combination of low yield reduction and high GM in Kamokamo indicates that it is physiologically better at transforming water to carbon, compared to the root and tuber crops studied. High GM and low DI I and PR in Table 4.4.1 are indices for selecting crops that are tolerant to environmental stress (de Souza Lambert et al., 2006) . Noticeably, Kamokamo had a high yield potential, compared to all other crop cultivars, under both environments. However, IWUE was high in modern potato ( Moonlight and Agria), whilst Kamokamo was comparable to Moe M oe, Buttercup squash and Dark O range IWUE , despite its high yield potential. Modern potato almost doubled IWUE, compared to Kamokamo, Moe M oe, Buttercup squash and D ark orange oca. Similarly, the yield reduction reflects that the modern potato was very sensitive to water stress (Shock et al., 2007), compared to the heritage potato, pumpkin squash and Scarlet oca. In spite of this fact, the yield reduction of potato was less than that documented by Ferreira et al. (2007), thus confirming that the yield reduction was moderate. Potentially, the modern potato cultivars and Dark Orange oca could reduce their yield beyond this stage, with DII over 0.7 (Ramirez - Vallejo et al., 1998) . The IWUE in potato shows that it varies with genotype , such as Tutaekuri, which does not respond to water application, possibly due to species differences and low HI. The moderately poor IWUE of Tutaekuri confirms the previous glasshouse trial results, which found that Tutaekuri was un responsive to 100 % ET , due to the same reasons (Chapter 3). CHAPTER 4 Field experiment on potato, oca and pumpkin squash 134 4.3.4.4.3 Water footprint of growing heritage and modern crop production Water footprint components differed with crop type or cultivars and water regimes, which have also been reported in various energy crops (Gerbens - Leenesa et al., 2009b) . Pumpkin squash, Kamokamo, was the most efficient crop cultivar, whilst Dark O range oca was the least efficient crop, on a water productivity basis (Fig. 4.4.1). The total water footprint of pumpkin squash cultivar was comparable to Moonlight , but it was almost five times smaller than WF of growing oca . Similarly, Moonlight, Agria and Moe M oe had comparable benefits on WF , compared to Tutaekuri ; where the WF was double that of other potato cultivars. Tutaekuri and pumpkin squash cultivars were more beneficial under rain- fed than irrigation. Otherwise, no advantage was identified for growing oca, except in the case of a promising premium price, which would countera ct low water productivity, compared to potato and pumpkin squash. The average total WF , which varied with cultivar, ranged from 46 m3 ton- 1 to 335 m3 tonne- 1 . A comparison of the WF of producing potato with results reported in the Netherlands (72 m 3 tonne- 1 ), USA (111 m 3 tonne- 1 ), Brazil (106 m 3 tonne- 1 ) and Zimbabwe (225 m 3 tonne- 1 ) (Gerbens - Leenes et al., 2009b) , show s that the water footprint of all four potato cultivars was greater than that for the Netherlands and almost equal to USA and Brazil , except for Tutaekuri, which was equal to the WF of growing potato in Zimbabwe. Furthermore, this study shows that the water footprint for producing potato and pumpkin squash in New Zealand is either within, or smaller than that of crops with the smallest water footprints in referred regions. Oca, which had the largest total water footprint in this study, is within the range of crops with the smallest water footprints: sugar beet, sugarcane and maize, reported in Netherlands, USA, Brazil and Zimbabwe (Gerben s- Leenesa et al., 2009b) . The average WF of growing Agria, Moonlight, Moe M oe, Tutaekur i, Buttercup squash, Kamokamo, dark orange and S carlet oca, correspondingly relates to 12, 10, 11, 20, 7, 5, 35 and 28 l of virtual water content, in order to produce 100g. The virtual water content for potato and pumpkin squash is lower than the 25l / 100g for potato tuber (Hoekstra et al., 2007) and the 23.8l / 100g for pumpkin (Kumar et al., 2007), which were estimated as mean global and Indian virtual wate r content, respectively. The virtual water content to produce oca was greater than the 25l / 100g for potato tuber. The average WF of this CHAPTER 4 Field experiment on potato, oca and pumpkin squash 135 study is also smaller, compared to the 1995 - 2006 global WF of pumpkin squash (336 m3 tonne- 1 ) and potato (287 m 3 tonne- 1 .) ( Mekonnen et al., 2010b) . The results suggest that there are great disparities in virtual water content and WF within global averages, which may be due to climate, cultivars and methodological differences, when estimating crop water use (Kumar et al., 2007; Hoekstra et al., 2007) . This study used actual water use and actual yield, as suggested by Maes et al. (2009), whilst the study referred to used hypothetical crops and water (Gerbens - Leenes et al., 2009a ) . On the other hand, the virtual water content and WF , in this study, outweigh the global WF put forward by Mekonnen et al. (201 0b) , where actual water use was used, thus proving some level of sparing water use, compared to other parts of the world. These attributes could be due to efficient agricultural practices, crop cultivars and good weather patterns in this particular study and year as formerly suggested by Hoekstra et al. ( 2007) . From the irrigated crops, it was apparent that blue water increased total crop water use by 34%, 48% and 59% , in oca, potato and pumpkin squash cultivars, respectively. As a consequence, blue water evidently raised the total water footprint of the total yield in Moe M oe, Tutaekuri, Buttercup squash, Kamokamo, and Scarlet oca by 5%, 45%, 28%, 25% and 8%, as also reported in wheat, whilst reducing the total water footprint of total yield in Agria, Moonligh t and dark orange oca by 6 %, 4% and 7%, as also reported in sugarcane and soybean, respectively (Mekonnen et al., 2010b). Irrigation was essential in reducing the total WF , by increasing total and marketable yields, especially in crop varieties that were very responsive to irrigation or sensitive to water stress. However, irrigation increased actual evapotranspiration and nearly potential evapotranspiration in Mo e M oe, Tutaekuri, B uttercup squash, Kamokamo, and s carlet, despite increasing a yield that raised their total WF. This highlights that irrigation is indispensable for yield quality improvement in crops with high IWUE and when rainfall is limited for most modern crops (Fabeiro et al., 2001; Kang et al., 2002) and some heritage crops, such as Moe Moe and oca . 4.3.4.4.4 Economic water productivity The EWP was highest under limited water, except with Moonlight. Battilani et al. (2004) and Zoebl (2006) also reported that crop water productivity was higher in rain- fed than in well watered crops. In this study, Moonlight show s that its EWP was not limited to CHAPTER 4 Field experiment on potato, oca and pumpkin squash 136 increased water allocation, due to its high IW UE reported previously. However, the average value obtained, per unit of water allocated to different crops, was greatest in Kamokamo and Moe M oe, due to their large yield and high market value. In this case, EWP is related to crop yield potential and market prices and other related water management factors (Molden et al., 2001) . The average economic water productivity values in equivalent to 20.4 US$/m 3 (2.70 to 38.10 US$/m 3 ) are twenty - fold those reported in 23 irrigated crops in Asia, Africa and Latin America, with a range of 0.03 to 0.91 US $/m 3 (IW M I, 2002 ) . Potato has been reported to have 0.3 US$/m 3 in Jordan (Molden et al., 2001; FAO, 2003) . These findings confirm a great spatial variation in economic water productivity between and within crops and regions, due to variations in crop management, marke t value and weather (Kumar et al., 2007; Hoekstra et al., 200 7) . Adoption of the information on IWUE, WF and EWP for various crops under rain- fed and irrigation regimes can help growers to allocate water more efficiently. The selection of cultivars can be based on IWUE, EWP and WF for particular water regimes or technology available (Hoekstra et al., 2009) . I rrigation water use efficiency and EWP indicate that modern potato has a comparative advantage under irrigation, than pumpkin squash, Moe M oe, and T utaekuri under rain- fed. However, irrigation is very essential for Moe M oe, oca and pumpkin squash for increased marketable yield and income and for a reduction in unanticipated drought risk and poverty (S IW I et al., 2005) . 4.4 Summary and Conclusion The field study indicates that irrigation influences total yield, marketable yield production and values of WF and EWP , for both heritage and modern crop cultivars differently, depending on their water extraction capacity, their ability to transform water to carbon and how they partition these assimilates to economic organs. The majority of heritage cultivars extract and synthesise more total assimilates. H owever, they prioritise allocation of assimilates to vegetative growth, compared to modern cultivars that optimise partitioning of assimilates to the harvestable part. This study also suggests that pumpkin squash has the highest yield potential and economic water productivity, due to its ability to use water efficiently within a short CHAPTER 4 Field experiment on potato, oca and pumpkin squash 137 lifespan, whereas Moe M oe is the potato highest EWP , due to its premium market value and its ability to modify harvest index with irrigation application. It was also observed that the modern potato is recommended more for irrigation, compared to pumpkin squash and Tutaekuri, due to their high IWUE and sensitivity to water stress. This indicates that where water is limited, selection of crops should be based on high yield potential, plus EWP and low WF (as noticed in Kamokamo and Moe M oe), or optimisation of irrigation water should be based on crops that have a high IWUE (as observed in modern potato). O ther crop cultivars did not need irrigation even when water was limited, due to their hereditary makeup (as observed in Tutaekuri) . O thers need irrigation due to their long lifecycle, which was affected by weather variability (as observed in oca). Consequently, the growers? final choice of enterprise need s to be based on a combination of market demand, crop water productivity and water availability. CHAPTER 4 Field experiment on potato, oca and pumpkin squash 138 CHAPTER FIVE Taewa and Agria response to irrigation and N 139 CHAPTER 5 COMPARISON IN THE FIELD OF YIELD AND WATER USE EFFICIENCY OF TAEWA AND A MODERN POTATO CULTIVAR 5.1 Introduction The results of the glasshouse experiment described in Chapter 3 and the field experiment described in Chapter 4 established that Moe M oe, one of the Taewa cultivars, responded to full irrigation and it competed favourably with modern potato cultivars, in tuber yield and WUE . In contrast , Tutaekuri ( S. andigena) did not respond to full irrigation compared to its counterpart, Moe M oe. Tutaekuri ?s poor response to irrigation was unexpected because potatoes usually respond to irrigation, perhaps due to specie difference (Bowen, 2003; Kang et al., 2004; Shock et al., 2007) . Subsequently, it was assumed that a low N and partial irrigation would interactively stimulate Tutaekuri to perform in the same way as Moe M oe and modern cultivars, under irrigation. This assumption is based on the fact that modern cultivars are bred for high yield, WUE and NUE while old or wild cultivars have low WUE and NUE because they were self- selected for adverse condition (Zebarth, et al., 200 8; Siddique et al., 1990a ). I rrigation and N enhance modern potato tuber yields and tuber quality ( Shock et al., 2007) . Presently, studies show that 200 - 300 kg N ha - 1 with 500 - 700 mm of water is the best rate for modern potato production in New Zealand (Craighead et al., 2003) . 200 - 250 kg N ha - 1 is recommended for short season crops and 300 kg N ha - 1 for long season crops. Hayward (2002) undertook a preliminary study of the effect of N on Taewa yield and this study indicated that there was no yield response to an increase in N . Given that the response of potato to soil moisture and N use is mainly influenced by genotypes (Laurence et al., 1985; Steyn et al., 1998) , N and water application need to be matched to Taewa growth habits, or otherwise their yield will not improve. S ignificant differences in tuber yields, between Taewa and modern cultivars, have been reported by Harris et al. ( 1999) and chapter 3 and 4. However, studies of Taewa have not considered irrigation and N concurrently in the field. Consequently, a field experiment was conducted , in order to determine the effect of irrigation and N regimes CHAPTER FIVE Taewa and Agria response to irrigation and N 140 on vegetative growth, dry matter partitioning, photosynthetic WUE, tuber dry matter and SG characteristics, N leaching, tuber yield, WUE and N UE in Taewa, in comparison with the modern cultivar, Agria , in the field . 5.2 Material and Methods 5.2.1 Experimental site The field experiment was conducted at Massey University?s Pasture and Crop Research Unit, Palmerston North, New Zealand. It was p lanted on 27 th October 2010 and harvested on 16 th April, 2011. The s oil is a Manawatu sandy loam soil. The detailed soil chemical characteristics, at the beginning of the experiment , are presented in Table 5.1. The soil samples were analysed at Massey University?s Fertilizer and Lime Research Centre. Total available N was <30 kg N ha - 1 . The maximum and minimum temperatu re, cumulative evapotranspiration and rainfall (mm) for the site during the October 2010 to April 2011 season are presented in Figure 5.2. Table 5. 1 Soil chemical properties at the beginning of experiment, October , 2010 5.2.2 Experimental design and treatments The field experiment was a Randomised I ncomplete B lock S plit- Split- Plot Design (R IBD S plit- Split- Plot) with three water regimes as the main treatments, three potato cultivars (Agria, Moe M oe and Tutaekuri) as sub- treatments and two N levels of N 1=80 and N2=240, as sub- sub- treatments; this was replicated four times (Figure 5.1). The three water regimes were (1) r ain- fed (P e); (2) partial irrigation (PI) ; and (3) full irrigation treatment (FI) . The FI received 25 mm irrigation at 30 mm soil moisture deficit ( SMD ), from plant emergence to crop physiological maturity. Irrigation was not applied to the PI treatment at the first irrigation of the FI treatment and was then irrigated at every second irrigation of FI. CHAPTER FIVE Taewa and Agria response to irrigation and N 141 Figure 5. 1 Schematic diagram for the field layout of E xperiment 3 for irrigation and nitrogen treatments of Taewa and modern potato cultivars CHAPTER FIVE Taewa and Agria response to irrigation and N 142 5.2.3 Irrigation and crop management 5.2.3.1 Fertiliser and plant protection The potatoes received 12N:5.2P:14K : 6S +2 M g+5 Ca, using 500 kg ha - 1 Nitrophoska Blue TE at planting . All plots received the same amount of fertiliser at planting and this was followed by 20 and 180 kg N ha - 1 of urea (as a side dressing) on 10 th December, 2010, in treatment N1 and N2, 24 days after emergence, respectively . Mounding was undertaken following the side dressing on 10 th December, 2010 , by using a tractor to embank the crop and control weeds . H erbicides were not used to control weeds and secondary weeds were manually controlled. Avermectin B1a (Avid or abamectin) and imidacloprid chloro- nicotinyl 700 g/kg ( Confidor 70WG ) were sprayed interchangeably every 10 - 14 days, in order to protect the potato from sucking and biting insect pests: leaf suckers and leafhoppers ( Empoasca fabae ), mites, and potato psyllid ( Bactericera cockerelli ) (A ppendix 7.3) . Chlorothalonil Tetrachloroiophthalonitrile (Bravo ULTREX SDG90), a broad spectrum fungicide, was sprayed to control fungal (late blight, Phytophthora infestans ) and bacterial diseases, together with Avid and Confidor. A number of plants displayed potato psyllid symptoms ( psyllid yellows) and presence of psyllid eggs, adult psyllids and pysllid nymphs underside leaf after 110 and 140 days after pl ant emergence (Roskruge , 2011 P ers comm.). Consequently, all the plants infested were visually scored for severity of symptoms and presence of any form of psyllid, on a scale of 0 ? 5, where, 0 is for no infestation and 5 for highly infested plots (Table 5.3) . Potato psyllid were identified according to Roskruge et al. ( 2010) . 5.2.3.2 Irrigation scheduling and irrigation depth Full irrigation treatment received 25 mm irrigation at 30 mm SMD , between 4 th December, 2010 and 20 th March, 2011. Full irrigation plots received seven irrigations, whilst PI plots received three irrigations. Irrigation was applied with a Trail boom traveller irrigator (Plate 5.2 a) and crop water use for irrigated and rain- fed treatments was determined by the soil water balance approach (Allen et.al., 1998 ), whilst soil moisture measurements were taken by TDR [ model 1502C, Tektronix Inc., Beaverton, OR, USA] , as described in Chapter 4. The actual water distribution within each plot was monitored (at every irrigation) by using a number of catch cans. The catch cans were CHAPTER FIVE Taewa and Agria response to irrigation and N 143 laid longitudinally at 0.5 m apart. At the end of the irrigation period, water trapped in the cans was measured and recorded. The irrigation depth for a particular plot was determined as an average of the water depth in the catch cans from each plot. 5.2.4 Plot size and plant spacing Potato tubers were manually planted on 27 th October, 2010, at 75 cm spacing between rows and 30 cm spacing within rows, at a depth of 10 - 15 cm. Each plot was 3 m by 1.5 m, containing 18 plants , and contained two guard rows planted with the same potato cultivar, except Tutaekuri, where Moe M oe was used as guard crop, due to insufficient seed potatoes (Figure 5.1 and Plate 5.1b) . 5.2.5 Growth morphological and gaseous exchange characteristics measurements Vegetative growth characteristics were measured on plant height (cm) ; number of stems per plant; number of branches per plant ; and stem diameter at soil collar (mm), 120 days from planting. G aseous exchange was measured once, at 90 DAE , using CIRAS - 2, which is a portable photosynthesis system ( V2.01) , describe d in chapter 3 . Photosynthetic WUE (?mol Co2 /m molH 2 O ) was determined as the ratio of net photosynthesis to transpiration rate as described in chapter 3 (Liu et al., 2006a ) (Plate 5.1a ) . Plate 5. 1 Gaseouse exchange and Leaf water potential measurements (a) Gaseous exchange measurements by CIRAS - 2 (b) Leaf water potential measurements by Pressure chamber CHAPTER FIVE Taewa and Agria response to irrigation and N 144 Leaf water potential ( ?w) was measured using the Scholander pressure chamber method [Soil Moisture Equipment Corp., Santa Barbara, CA, USA] on both irrigated and non- irrigated plants (Boyer 1995) . L eaf water potential was measured in the morning (6:00 - 8: 00 am) at the development crop stage (Plate 5 .1b ) . Above- ground (leaves and stems) and below - ground biomass (roots and tubers) were sampled between 14 th and 18 th February 2011, which was 120 days after planting. A small and a large plant sample were randomly uprooted from each plot, by using a spade. The plants were thoroughly washed, a nd then partitioned into leaves, stems, roots and tubers and weighed and oven dried at 70 oC, until there was no further weight loss. The contribution of each component to total biomass was determined as the ratio of each component to total biomass (leaves, stems, roots and tubers), per plant. Root : shoot ratio was determined as dry weight for roots divided by the dry weight of the above- ground biomass (leaves +stems biomass) (Siddique et al., 1990b) . Harvest index was calculated 1 20 DAP , as the ratio of total tuber yield to total biomass production from the samples of each plot (Mackerron et al., 1985) . Detailed procedures for vegetative growth, dry matter production and partitions per plant, and gaseous exchange characteristic measurements are described in Chapters 3 and 4. 5.2.6 Soil water sampling procedure for nitrogen leaching measurements In a very preliminary measure of N leaching, s oil water samples were collected from the 24 plots of FI and 24 plots of rain- fed treatments, during summer and winter season. Half of the plots in each water regime received high N, whilst the other half received low N for all three potato cultivars. Nitrogen leaching was monitored using forty- eight porous ceramic suction cup samplers (Curley et al., 2011) . These cups were 75 mm long and 22 mm in diameter, cemented onto a 22 mm outside diameter PVC pipe, 60 cm in length. The porous ceramic suction samplers were installed at a depth of 30 cm in holes made by a soil auger at the middle of each plot, one week after planting. The suction cups and soil media hydraulic contact and stability were enforced by slurry from the augured soil before and after inserting the suction probe. PVC cups were used to close the PVC end. A manual vacuum pump made from high quality material was used to create a vacuum in samplers, 24 - 48 hrs before sampling. The vaccum was maintained with a rubber stopper. After 24 - 48 hrs, the soil water in the PVC tubes was siphoned with a 50 ml CHAPTER FIVE Taewa and Agria response to irrigation and N 145 syringe connected to a length of polythene tube. The siphoned samples were transferred into a well tagged plastic flask, which was stored frozen, prior to laboratory analysis. Sampling was conducted on several occasions during irrigation and after heavy rain. Laboratory analysis was conducted on the ammonium- N (NH4 + - N O 3 ) and nitrate - N (NO 3 - N) content , by using a Technicon II Auto- Analyser ( the Ammonium- N itrate procedures) at the Fertilizer and Lime Research Centre (FLRC) within the Institute of Natural Resources, Massey University , Palmerston North (Technicon, 1976; Downes, 1978) . Nitrate - N leaching was estimated per ha by multiplying the Nitrate - N concentration of soil water samples by the drainage volume estimated using the soil water balance (Sumanasena, 2003). 5.2.7 Tuber yield and biomass production measurements 5.2.7.1 Total tuber yield, marketable tuber yield and final harvest index The potatoes were finally harvested on 16 th April, 2011 using a potato harvester . At harvest, the total fresh tuber yield per plot (kg) , marketable tuber yield per plot (kg) , number of tubers per plant, and average tuber weight per plant were measured. M arketable tuber s were those weighing above 55 g, without any damage while small, damaged tubers were categorized as non - marketable . Marketable potato tubers were not graded further (Plate 5.2cd) . Final HI was calculated, described in Chapter 4 (Mackerron et al., 1985) . 5.2.7.2 Water use efficiency indicators and statistical analysis Water use efficiency , economic water productivity, irrigation water use efficiency and water stress indicators were determined ( Chapter 4) . The data collected were analysed with the GLM procedure of the S AS (SAS, 2008) , differences amongst treatment means were compared with the LSD , at the 5% probability level (Meier, 2006) . The relationship between water use and tuber yield was investigated using regression analysis (Ferreira et al., 2007) . CHAPTER FIVE Taewa and Agria response to irrigation and N 146 The RIBD Split - Split- plot linear statistical model used in GLM procedure was: ?ijk = ? + ? i+? j +(??)ij +? k +(??)ik +(??) j k +(???)ijk + ?l + ( ???)ik l+????)ijk l+?ijk l ; Where, ? is the overall mean; ? i , ? j , (??)ij represents the whole plot as water regimes, block and whole plot error effects; ? k , (??)ik , (??) j k represents subplots as potato cultivars effects, block effects and subplot errors; (???)ijk represents whole plot and subplot interaction effects; ?l , ( ??? ) ik l , ????)ijk l represents the sub- sub plot as N , block effects and sub - sub plot errors; whole plot , subplot and sub- sub- plot interaction and ?ijk l represents overall error, respectively , whilst i= 1 - 3 water regimes, j=1 - 4 replicates, k=1 - 3 potato culti vars, l =1 - 2 represents N levels. Plate 5. 2 Outlook of irrigated Moe Moe and Tutaekuri potatoes in 2010/2011 season (a) Travel irrigator irrigating Taewa (b) Outlook of irrigated modern and heritage potato in the field in 2010/ 2011 season (c) Graded Moe Moe (d) Graded Tutaekuri CHAPTER FIVE Taewa and Agria response to irrigation and N 147 5. 3 Results 5.3.1 Crop evapotranspiration and soil moisture content 5.3.1.1 Cumulative potential evapotranspiration, precipitation, and mean temperature The growing seasons for Taewa and modern potato were 170 and 140 days , with potential crop water requirement s of 611 mm and 491 mm, respectively (Table 5.2; Fig . 5.2) . S easonal precipitation of 368 mm contributed 50 - 60% of the total crop water requirement (Fig.5.2). The average maximum and minimum temperatures, total solar radiation and average wind speed for the 2010/ 2011 season were 24.9 oC, 9 oC, 3395 ( MJ /m 2 ) and 291 (km day - 1 ), respectively. Figure 5. 2 Cumulative rainfall (mm), potential crop evapotranspiration (mm), monthly average maximum temperature and minimum temperature ( oC) for the experimental site during the growing season fro m October, 2010 - April, 2011 CHAPTER FIVE Taewa and Agria response to irrigation and N 148 5.3.1.2 Actual crop water use per irrigation scheduling The actual evapotranspiration for the full irrigation (FI), partial irrigation (PI) and rain - fed treatments (P e) averaged 523.4, 416.4 and 355.6 mm, respectively ( Table 5.2). Full irrigation and PI were irrigated seven and three times, respectively. The water use for FI, PI and P e treatments was 92%, 73 % and 60% of potential water requirement, respectively (P<0.0001). Consumptive water use (m 3 ha- 1 ) was greatest in FI and lowest in rain- fed treatment (Pe) , whilst PI was intermediate . Taewa used more water compared to the modern cultivar, Agria (Table 5.2 , Appendix 5.1b). Table 5. 2 : Precipitation (P e) ; irrigation (I) ; deep percolation (D p ) ; soil moisture change (?S); actual evapotranspiration (ET c ) ; and crop water use [ ETc or CWU = Pe + I ? D p + ?S ] from 27 th October, 2010 to 12 th April, 2011 5.3.1.3 Volumetric soil moisture content (%) Soil moisture content was signifi cantly influenced by cultivar (P<0.01), irrigation (P <0.0001) and number of days from planting (DAP) (P<0.0001; Appendix 5.1ab ) . Full irrigation increased soil moisture, followed by PI (Fig. 5.3 b) . Significant interactions with soil moisture were observed between irrigation*DAP (P<0.0001) cultivars*DAP (P<0.01) and irrigation*cultivars*DAP (P <0.01) ( Fig. 5.3ab; Appendix 5.1). CHAPTER FIVE Taewa and Agria response to irrigation and N 149 Figure 5. 3 C hange in volumetric soil moisture content (%) for (a) each cultivar and (b) water regime overtime. CHAPTER FIVE Taewa and Agria response to irrigation and N 150 Agria extracted more water between day 6 0 and 90 (Fig. 5.3a). Full irrigation increased soil moisture content, whereas N had no effect on soil moisture content (P >0.05). The interaction in soil moisture resulted from the differences in water inputs and cultivar water extraction differences and was highly noticed on day 80 (Fig. 5.3ab; Appendix 5.1). 5.3.2 Vegetative growth characteristics of Taewa and modern potato cultivars 5.3.2.1 Flower production and physiological maturity Both cultivar and water regime influenced date to flowering (P<0.0001; P <0.01; Table 5.3). Tutaekuri flowered earlier than Agria and Moe Mo e. Full irrigation delayed flower production. The time of flowering was not affected by N (P>0.05) . Agria and Taewa matured 140 and 170 days after planting, respectively. 5.3.2.2 Plant height (cm) Cultivars (P <0.0001) and N (P<0.01) influenced plant height but irrigation did not affect plant height (P>0.05; Table 5.3). Taewa cultivars were the tallest cultivars. The modern cultivar, Agria was the shortest. An increase in N greatly increased potato plant height by 7.5% (P<0.01) . There were cultivar*irrigation interactions observed on plant height (P<0.05). This interaction involved a decrease in plant height with PI in Moe Mo e, whereas Tutaekuri increased plant height with PI (Appendix 5.2a). 5.3.2.3 Number of main stems and secondary branches per plant Potato cultivars, irrigation and N regimes influenced the number of stems (P<0.0001, P<0.05, P<0.05) and branches per plant (P<0.001 , P<0.05, P <0.001) (Table 5.3). Agria had more main stems with fewer branches per plant than Taewa. However, the number of branches per plant in Tutaekuri was more than ten times those in Agria (Table 5.3). There were interactions between potato cultivars and the water regime on the number of stems per plant (P <0.05 ) and the number of branches per plant (P <0.001) : and also between the water regime and N on the number of branches per plant (P <0.05). These interactions were caused by an increase in stems and branches per plant in Agria and Tutaekuri, respectively, after rainfall. High N also increased stems per plant in Taewa with the greatest increase being observed in Tutaekuri, whereas Agria had a constant number of stems (Appendix 5.2b- d). CHAPTER FIVE Taewa and Agria response to irrigation and N 151 Table 5. 3 Vegetative growth characteristics and potato psyllid scores at 110DAE and 140DAE in three potato cultivars under different water nitrogen regimes in the field, 2010/ 2011 6.3.1.4 Stem diameter (mm) Water regime and N did not influence stem diameter but the cultivars showed different diameters ( P<0 .01; Table 5.3) . Tutaekuri had the largest stem diameter s. Agria stem diameter was the smallest and Moe Moe was intermediate. Usually, Taewa had wider stems than modern cultivar, Agria (Table 5.3 ) . 6.3.1.5 Potato psyllid 4 infestation Potato psyllid infestation was visually scored in late February and late March, 2011 (Table 5.3) . At 110 DAE there were significant differences between potato cultivars for potato psyllid infestation (P<0.0001), but not between irrigation and N treatments 4 Potato psyllid is a vector of the bacterium ? Candidatus Liberibacter solanacearum? which causes the disease zebra chip and other problems in potatoes (Plate 5.3), tomatoes and tomaliros. CHAPTER FIVE Taewa and Agria response to irrigation and N 152 (P>0.05). Agria was highly infested by potato psyllid by February, whilst Taewa had shown some resistance by that time. At 140 DAE psyllid scores were influenced by irrigation, N and cultivar (P<0.05, P<0.0001, P<0.0001, respectively ) . Full irrigation and N enhanced potato psyllid infestation, lowest score was observed in Tutaekuri . There were interactions between cultivar* irrigation and cultivar *N regimes (Table 5.3; Appendix 5.3). Simple correlation of potato psyllid, with total tuber yield with all data combined, found that potato psyllid were strongly negatively correlated with total tuber yield (P <0.0001, r = - 0.57). Potato psyllid infestation was high in FI for all cultivars and low under rain- fed in Taewa, whilst Agria had high average potato psyllid infestation. Nitrogen increased potato psyll id potentially through increased leaf area and this increase was very high in Agria, compared to Taewa (Appendix 5.3). Plate 5.2 displays the symptoms of potato psyllid infestation appeared in each of the three potato cultivars. Plate 5. 3 : Potato pysllid symptoms in Agria, Moe Moe and Tutaekuri, 2011 5.3.3 Photosynthetic water use efficiency and gaseous exchange Cultivar significantly influenced photosynthetic WUE, A n, g s and Ci (P<0.01, P<0.05, P<0.05, P<0.01), but not T (P>0.05, Table 5.4). Taewa had the highest photosynthetic ( CHAPTER FIVE Taewa and Agria response to irrigation and N 153 WUE , An, g s and lowest Ci, especially Moe Moe . Irrigation significantly affected An, gs, T and Ci (P<0.05, P<0.01, P<0.05, P<0.05), but not photosynthetic WUE (P>0.05) whereas, N significantly influenced A n and gs only (P<0.05, P<0.01 ). Increased irrigation and N increased An, and gs, whilst decreasing Ci , except for N . Rain - fed treatments had restricted gs and T, resulting in low An. However, Ci increased with PI treatment. The high Ci in PI was accompanied by high g s. , whilst low Ci in rain- fed treatment was accompanied by the lowest gs. Similarly, high Ci in Agria was accompanied by low gs. The highest Ci was in Agria with partially irrigated treatments (P<0.01, P <0.5) . Nitrogen influenced A n and gs (P<0.05), but did not affect Ci, photosynthetic WUE and T (P>0.05; Table 5.4). Table 5. 4 Photosynthetic WUE , net photosynthesis (A n), stomatal conductance (g s ) transpiration (T), and internal carbon concentration (C i ) in Taewa and modern potato cultivars under different water and N regimes at 90DAE CHAPTER FIVE Taewa and Agria response to irrigation and N 154 5.3.4 Leaf water potential (?w) L eaf water potential ( ?w) was significantly influenced by water regime ( P<0.0001) and cultivar (P < 0.05, Table 5.5 ). The rain - fed treatment had the lowest leaf water potential, compared to fully and partially irrigated treatment. Agria had the smallest leaf water potential amongst the three cultivars, lower than Tutaekuri , but not different from Moe M oe. Nitrogen levels did not af fect the leaf water potential (Table 5.5) . Table 5. 5 Effect of water and N regimes on leaf water potential (bars) in Taewa and modern potato cultivars, 2010/ 2011 5.3.5 Dry matter production and partitioning The total dry matter production per plant was not significantly different between cultivars, irrigation and N (P>0.05, Table 5.6). However, partitioning of assimilates into leaves, stems, roots and tubers statistically differed between cultivars ( P<0.0001) . The water regime significantly enhanced tuber dry matter production (P <0.00 01) , whilst N significantly increased leaf and stem dry matter production per plant (P <0.05). F ull irrigation almost doubled tuber dry matter production per plant (Table 5.6) . Increased N reduced tuber dry matter production per plant in Taewa, whilst increasing it in Agria (Table 5.6). CHAPTER FIVE Taewa and Agria response to irrigation and N 155 Taewa had more leaves, stems and roots , whilst the modern cultivars had more tuber biomass per plant. Tutaekuri allocated 30% to leaves, >36% to stems and >8% to roots compared to Agria, which translocated >60 % to tubers and the least to leaves, stems and roots (P <0.0001) , whilst Moe M oe was intermediate. Generally, Agria significantly partitioned a small portion to shoots and roots compared to Taewa. The HI after 120 DAP differed with cultivars, water and N regime (P<0.00 01, P<0.001, P<0.01, Table 5.6. The h ighest HI for Agria reflected its ability to allocate dry matter to the tubers. Taewa had a significant amount of roots and root: shoot ratio compared to the modern cultivar (P<0.05) (Table 5.6). There were significant interactions between cultivar*N and cultivar*water regime on HI (P<0.05, Fig. 5.4). The decrease of HI with rain- fed treatments and the HI increase with irrigation caused t he interaction between water regime and cultivars on HI . The interaction between N and cultivar was caused by a decrease in HI with N increase in Taewa, whilst it increased in Agria. (Fig. 5.4) CHAPTER FIVE Taewa and Agria response to irrigation and N 156 Table 5. 6 Effect of water and nitrogen regimes on leaf , stem, root, tuber and total biomass on fresh and dry matter basis per plant (g) in three potato cultivars, 2010/ 2011 CHAPTER FIVE Taewa and Agria response to irrigation and N 157 Figure 5.4 Interaction between potato cultivars and water regime (a); and interaction between potato cultivars and nitrogen (b) on HI% during biomass sampling . Error bar represents ?SEM. CHAPTER FIVE Taewa and Agria response to irrigation and N 158 5.3.6 Tuber yield and yield components The number of tubers per plant, mean tuber weight for total and marketable tubers (g) , total tuber, marketable tuber yield (t ha - 1 ) and final HI, were strongly influenced by cultivar (P<0.0001), irrigation ( P<0. 001) and N (P<0.0001, Table 5.7). Agria had the lowest number of tubers per plant. However, it had a higher mean tuber weight , H I and total and marketable tuber yield than Taewa cultivars. Tutaekuri had the highest number of tubers and lowest mean tuber weight, HI , and total and marketable tuber yield. Moe Moe was intermediate in all attributes, although the number of tubers per plant were not different to Agria (P>0.05, Table 5.7). Irrigation increased the number of tubers per plant (P<0.0001); mean tuber weight (P<0.05); total tuber yield , HI (P<0.001) and marketable tuber yield (P<0.0001), but did not increase the mean marketable tuber weight (g) (P>0.05). Partial irrigation had a high number of tubers per plant whilst FI increased mean tuber weight; total tuber yield; and marketable tuber yield differ ently from PI and rain- fed. Full irrigation increased the number of tubers per plant; mean tuber weight; total tuber yield; and marketable tuber yield by 18%, 6%, 43% and 49%, whilst PI enhanced them by 24%, 6%, 26% and 13%, respectively (Table 5.7). Other wise, high N decreased the number of tubers; total tuber yield; marketable tuber yield; and final HI by 16%, 17%, 14% and 12% respectively (P<0.0001). On the other hand, N did not enhance average tuber weight and final HI (P>0.05). CHAPTER FIVE Taewa and Agria response to irrigation and N 159 Table 5. 7 Effect of irrigation and N regimes on tuber yield (t ha - 1 ) and yield components in Taewa and modern potato cultivars, 2011 Note: WR refers to water regime, N refers to nitrogen , and column rows with same letters are not significantly different at 5% level of probability. CHAPTER FIVE Taewa and Agria response to irrigation and N 160 Figure 5. 5 (a) Interaction between water regime*cultivar ; ( b) interaction between cultivar * nitrogen, on number of tubers per plant: Error bar represents ?SEM. CHAPTER FIVE Taewa and Agria response to irrigation and N 161 There were significant interactions between cultivars and irrigation on the number of tubers per plant (P<0.0001, Fig. 5.5a); total tuber yield (P<0.0001); and marketable tuber yield (P<0.0001, Fig. 5.7). Cultivar and N significantly interacted on the number of tubers per plant (P<0.01, Fig. 5.5b); mean tuber weight (P<0.05, Fig. 5.6); final HI (P<0.001); and total and marketable tuber yield (P<0.0001, Table 5.7). Significant interactions were also observed between cultivar, irrigation and N on final HI (Fig.5.9) and total and marketable tuber yield (P<0.01) (Fig. 5.8). No interactions were observed between irrigation and N (P>0.05), apart from HI (P<0.05). The interaction involving the number of tubers per plant was a consequence of tuber decrease with FI and rain - fed, whilst it increased with PI in Tutaekuri. In other cultivars, the number of tubers decreased from FI to rain - fed (Fig.5.5a). Nitrogen reduced tuber number in Taewa but not in Agria (Fig. 5.5b). The mean tuber weight in Agria increased with N increase, whereas Taewa decreased its mean tuber weight with N increase (Fig. 5.6). Figure 5. 6 Interaction between nitrogen and potato on mean tuber weight (g). Error bar represents ?SEM . CHAPTER FIVE Taewa and Agria response to irrigation and N 162 Figure 5. 7 Interaction between water regime and cultivar (a), and nitrogen and potato cultivars (b) on total tuber yield. Error bar represents ?SEM. (a) CHAPTER FIVE Taewa and Agria response to irrigation and N 163 Similarly, total and marketable tuber yield in Agria increased with high N, whilst Taewa decreased tuber yield with high N (5.7b). Water stress under rain- fed decreased the response of potato cultivars to N (Fig. 5.8). Tutaekuri performed better under PI compared to FI and rain- fed, whilst others performed w ell under FI (Fig.5.7a). Interaction on final HI involved an increase in final HI with high N for partially irrigated Moe Moe and Agria, whilst other irrigation scenarios reduced final HI with high N (Fig.5.9). Figure 5. 8 I nteraction between cultivars, irrigation and nitrogen regime on total tuber yield (t ha - 1 ). Error bar represents ?SEM. CHAPTER FIVE Taewa and Agria response to irrigation and N 164 Figure 5. 9 Interaction between water regime, nitrogen and potato cultivars on final HI. Error bar represents ?SE M. 5.3.7 Water use efficiency, economic water productivity and nitrogen use efficiency W ater use efficiency mirrored tuber yield, whereas economic water productivity (EWP in NZ$ /m 3 ) reflected the product marketable value, in addition to tuber yield (Table 5.8). W ater use efficiency was highest in Agria and lowest in Tutaekuri, whereas Moe Moe was intermediate (P<0.0001). W ater use efficiency was significantly influenced by water regimes (P<0.001 ) and N (P<0.0001 ) in all cultivars, although differently. W ater use efficiency was highest under PI and low N , whereas FI was the least in WUE . Rain - fed treatment was intermediate though not statistically different from both PI and FI (P>0.05). Full irrigation decreased WUE, whilst PI increased it in all cultivars (Fig. 5.10). W ater use efficiency decreased with increasing N in Taewa and rain - fed Agria, whereas PI and FI did not reduce WUE at high N in Agria (P<0.01, Fig. 5.10). Economic wat er productivity was highest in Moe Moe and lowest in Tutaekuri, whilst Agria was intermediate (P<0.0001, Table 5.8). Partial irrigation and low N increased EWP, CHAPTER FIVE Taewa and Agria response to irrigation and N 165 whilst FI and high N decreased EWP (P<0.01, P<0.0001). The interaction involving EWP resulted from the increase in EWP at high N and PI in Agria, whereas Taewa had decreased EWP at high N (Fig. 5.11). Ni trogen use efficiency was significantly high for Agria, (P<0.0001), FI (P<0.0001) and low N (P<0.0001; Table 5.8; Fig. 5.12). Tutaekuri, rain- fed and high N treatments had the lowest NUE. There were interaction effects between water regime*cultivars (P<0.0001); water regime*N (P<0.01); cultivars*N (P<0.0001); and cultivar*water regime and N on NUE (P<0.05) (Fig. 5.12). Full irrigation increased NUE in Agria and Moe Moe, whereas PI increased NUE in Tutaekuri. High N decreased NUE by over 300%, whereas rain- fed decreased it by 40% (Table 5.8). Partial irrigation had an intermediate influence on NUE in Moe Moe and Agria (Fig. 5.12 ). Figure 5. 10 Interaction between cultivars, irrigation and nitrogen regime on WUE (kg ha- 1 m3 ). Error bar represents ?SEM. CHAPTER FIVE Taewa and Agria response to irrigation and N 166 Table 5. 8 Water use efficiency (WUE), nitrogen use efficiency (NUE) and e conomic water productivity (EWP) (N Z$/m 3 ) for Taewa and modern potato cultivars under different water and nitrogen regimes, 2010/ 2011 Note: Columns with same letters are not significantly different at LSD 0.05 CHAPTER FIVE Taewa and Agria response to irrigation and N 167 Figure 5. 11 Interaction between cultivars, irrigation and N regime on EWP (NZ$ m - 3 ). Error bar represents ?SEM. Figure 5. 12 Interaction between cultivars, irrigation and N regimes on NUE (KgN kg - 1 ). Error bar represents ?SE M. CHAPTER FIVE Taewa and Agria response to irrigation and N 168 5.3. 8 Crop water production function for Taewa and modern potato 5.3.8.1 Irrigation water use efficiency (kg ha - 1 m- 3 ) and water stress index A regression analysis of total tuber yield and consumptive water use (CWU) with data stratified by cultivars indicated a general fresh tuber yield- water regime linear relationship (Appendix 5.4a bc). Agria, Moe Moe and Tutaekuri increased tuber yield with irrigation by 8.64? 1.24, 6.51?1.93 and 1.03?1.80 (kg ha- 1 m- 3 ), respectively. The relationship significantly differed in Agria (P<0.0001, r 2 = 0.687) and Moe Moe (P<0.01, r2 = 0.34), but it was not significant in Tutaekuri (P>0.05, r 2 = 0.015 (Appendix 5.4a bc) . Table 5.9 presents the stratification of data by water regime, to measure change in IWUE of different cultivars, when moving from one water regime scenario to another (i.e. rain - fed to partial irrigation and rain- fed to full irrigation), in order to gather information on irrigation optimisation. Agria had the highest IWUE when both FI and PI were compared with rain- fed system; however, it was the highest under PI. Cultivar significantly differed in IWUE when FI is compared with rain- fed system (P<0.0001) . However, N did not significantly affect yield, as production moved from rain- fed to PI or FI (P> 0.05 ). Moe Moe had high IWU E when FI was compared with rain- fed scenario, whilst Tutaekuri had high IWUE when moving from rain- fed to PI and not to FI (Table 5.9). The total yield geometrical mean and drought intensity index (DII) significantly differed under all scenarios (P<0.0001). The percentage of yield reduction (PR %) was significantly different under rainfed versus FI scenarios (P<0.0001). Geometrical mean was highest in Agria and lowest in Tutaekuri whilst PR% was highest in Moe Moe and Agria, and lowest in Tutaekuri. The water stress effect was highest when rain - fed production was opted out from FI, whereas GM was highest when FI production was opted out of rain- fed. The tuber yield reduction of rain- fed Agria, Moe M oe, and Tutaekuri were 32.9%, 2 8% and 9.2%, respectively, when rain- fed was opted out of FI . CHAPTER FIVE Taewa and Agria response to irrigation and N 169 Table 5. 9 Comparison of irrigation water use efficiency ( IWUE kg ha - 1 m- 3 ), drought intensity index ( DII ) , yield geometrical mean ( GM ) and yield % reduction (PR %) in Taewa and modern potato with different irrigation and N scenarios, 2010/ 2011 5.3.9 Specific gravity and tuber dry matter content Table 5. 10 Tuber dry matter (DM %) and specific gravity for Taewa and Agria, 201 1 CHAPTER FIVE Taewa and Agria response to irrigation and N 170 There were significant differences in SG, DM % and predicted starch between cultivars (P <0.0001) , but not between irrigation and N regimes (P >0.05, Table 5.10). Tutaekuri had the highest SG, predicted starch and DM % , whilst Agria was not different from Moe Moe ( Table 5.10). The results clearly indicate that the cultivar with high SG , Tutaekuri , had i ncreased DM % and predicted starch. 5.3.10 Nitrogen concentration and potential N losses in the soil water Nitrate - N (NO 3 ) concentration in soil water was influenced by the rate of N application (P<0.05), but it was not affected by the autumn season (Table 5.11). Ammonium - N (NH 4 + ) concentration in soil water was influenced by the autumn season (P<0.05), but it was not affected by the rate of N application. Irrigation had no effect on both ammonium- N (NH 4 + ) and nitrate - N (NO 3 ) concentrations in soil water. An application of 240 kg N ha- 1 increased nitrate- N concentration in the soil water from 1.2 (mg/ l) at low N to 2.9 (mg/ l) . There was a considerable ammonium concentration in soil during autumn (10.0 mg/ l) compared to the summer season (0.3 mg/ l). However, N concentrations were not significantly different between irrigated and rain- fed crops or between high N and low ( P>0.05; Table 5.11) . Potential N loss as leaching (kg N/ha) in summer and autumn were very small. CHAPTER FIVE Taewa and Agria response to irrigation and N 171 Table 5. 11 Effect of irrigation on nit rogen concentration and potential N loss in the soils grown with Taewa and modern potato cultivars CHAPTER FIVE Taewa and Agria response to irrigation and N 172 5.4 Discussion 5.4.1 Crop water use and soil water content The weather for Palmerston North in the summer 2010/ 2011 was characterised by high potential evapotranspiration and low rainfall. The volumetric soil moisture data indicate that the fully irrigated treatment maintained its water consumption closer to potential evapotranspiration, which is regarded as being crucial for the greatest yield in modern potato varieties (Ferr eira et al., 2007). In comparison, the rain - fed treatment failed to fully balance the water required by the plants , whereas the partially irrigated plants were maintained closer to full supply. Plant water extraction was more influenced by water availability than by genotypes. The differences in crop water use between Taewa and the modern potato cultivars, within the irrigation schedules, were due to their life span and physiological differences (Allen et al., 1998) . For the rain - fed crop, Taewa used more water (36 0 - 550 mm) than the modern cultivar, Agria (270 - 460 mm), as observed in the previous experiment (Chapter 4). Similar results have been recorded between old and modern wheat (Siddique et al., 1990a ) . The actual crop water use for FI (500 - 700 mm) was typical of reported values in irrigated potato (Allen et al., 1998; Shock et al., 2007) . Likewise , Chapter 4 (Section 4.3.1) provide s a potential evapotranspiration of 610 mm; this study determines 611 mm, as a benchmark for Taewa water requirement within New Zealand. However, the crop water requirement for Taewa will vary with the season and location, as reported for modern potato (Shock et al., 2007) , although the deviation may not be large, as observed in the 2009/ 2010 (Chapter 4) and 2010/ 2011 s easons. 5.4.2 Vegetative growth and dry matter partitioning characteristics Taewa cultivars were tall with a few main stems comprised of multiple branches and a large number of tubers per plant ( particularly, Tutaekuri), compared to the modern cultivar, Agria. Nevertheless, Taewa and Agria had equivalent total dry matter production per plant. The similarity in total dry matter was also observed in the previous field experiment (Chapter 4) . This result implies that the genetic potential for total dry matter production is consistently the same between Taewa and modern cultivar. The differences between these genotypes can be found in the allocation of assimilates to harvestable tubers, with modern potato allocating >60% to harvestable tubers, whereas CHAPTER FIVE Taewa and Agria response to irrigation and N 173 Taewa allocated <60% to harvestable tubers and the remainder to shoots and roots. This confirms the observation of Geremew et al. (2 007) that a cultivar with the highest canopy and LAI (Shepody) has a reduced tuber yield, compared to cultivars with a lower canopy and LAI. The latter were efficient in allocating more dry matter to tubers. These findings demonstrate that old cultivars partition more dry matter to non- harvestable organs, unlike modern cultivars that partition more to the harvested organs (Ziska et al., 2007) . Siddique et al. (1990a ) reported the highest HI in modern wheat cultivars and a comparable total shoot biomass between modern and old wheat cultivars. The lower root: shoot ratio observed in modern potato might have increased its HI, because modern potato cultivars have a high yield per unit root weight ( Sattelmacher et al., 1990), as also reported in modern wheat cultivars ( Siddique et al., 1990b) . Sattelmacher et al. ( 199 0) also confirmed that S.andigena has a higher root dry matter than other Solanum species. It is the objective of all crop breeders to increase HI as a way to increase total yield ? and this has been achieved in rice, wheat, barley, maize and potato. There is evidence that dry matter partitioning and HI also varied within the Taewa cultivars. Solanum andigena (i.e Tutaekuri ) had the largest sink, as observed in the current and the previous studies ( Kumar et al., 20 06). As a result, Tutaekuri had a lowe r harvestable component compared to Moe Moe, a s illustrated by their lowest HI durin g sampling and final harvesting. The low HI of Tutaekuri suggests that, within Taewa cultivars, a difference in partitioning assimilates to tubers exists, as it also does b etween modern and heritage potato cultivars. Full irrigation did not increas e HI in Tutaekuri, compared to Moe Moe. There were large increases in HI for Agria and Moe Moe with irrigation, thus indicating how partitioning and growth characteristics vary within Taewa cultivars and other potato cultivars with irrigation ( Tekalign et al., 2005) . However, the N increase decreased the HI of both Taewa cultivars, whilst increasing that of the modern cultivar, Agria. Nitrogen also consistently decreased HI in old cereal and potato genotypes, whilst increasing it in modern genotypes (Feil, 1992; Zebarth et al., 2008) . The reason for this occurrence is that N boosted the vegetative growth of Taewa, whilst reducing its NUE , which was very high in the modern cultivars ( Sattelmacher et al., 1990) . The low CHAPTER FIVE Taewa and Agria response to irrigation and N 174 partitioning of biomass to tubers in Taewa is an impediment to its adoption, otherwis e the late maturity in S.andigena cultivar (Kumar et al., 2006), such as Tutaekuri, could be advantageous in optimising solar radiation, compared to the modern cultivar, Agria . 5.4.3 Photosynthetic water use efficiency and gaseous exchange Comparable to the glasshouse and 2009/ 2010 field experiments, this study found that An and gs were influenced by cultivars, irrigation and N, as have other researchers (Olesinski et al., 1989; Tekalign et al., 2005) . Taewa achieved high photosynthetic WUE and An by maintaining high gs at low Ci, compared to Agria . Contrary, to the glasshouse observations, the high Ci in Agria was associated with low gs. Agria could not steadily increase An even when the T was comparable to the Taewa cultivar, Moe Moe because of high Ci. This result is in line with the report on greater photosynthetic WUE being found in old wheat cultivars, rather than in modern cultivars (Ko? et al., 2003) . Internal carbon concentration was the main cause of variations in photosynthetic WUE and gaseous exchange between Agria and Taewa, as previously observed in the glasshouse study (Chapter 3) . The relationship of Ci and photosynthetic WUE and A n was found to be inversely linear ( Figure 5.13a ; Morison, 1998). Figure 5.13b confirms that An and gs were curvilinearly related ( Vos et al. , 1989a ). Consequently, low g s and high Ci reduced An and photosynthetic WUE in Agria. L ow Ci and high gs in Taewa enhanced their photosynthetic WUE (Fig. 5.13b) . Consequently , Taewa and modern potato are different in gaseous exchange characteristics in the course of Ci and stomata conductance as observed in the glasshouse. D ifferences in growth stages between Taewa and the modern cultivar might prompt these variations in photosynthetic WUE at the time of the measurements. The characteristics of photosynthetic WUE for Taewa offer the potential ability for drought adaptation compared to the modern cultivar, Agria. Water and N deficits steadily decreased g s, as also reported by Schapendonk et al. (1989). Consequently , T and An reduced under rain- fed and low N, as reported by Olesinski et al. (1989) . In c ontrast to rain- fed, partially irrigated potato achieved the higher Ci, g s and T, which consequently increased photosynthetic capacity. On the other hand, FI moderately increased T and g s with reduced Ci and hence the high An. This CHAPTER FIVE Taewa and Agria response to irrigation and N 175 suggests that water stress decreased gs whilst partial stress reduced the resistance with great T and Ci fluxes. Full irrigation stabilis ed gs, Ci and T , resulting in high An. Consequently, photosynthetic WUE was not statically different between water regimes though FI was greater than PI , despite its high An. The high fluxes in Ci and T under PI reduced its photosynthetic WUE. This finding confirms that water and N deficiencies limit photosynthetic capacity ( Olesinski et al., 1989), whereas FI and PI improve photosynthetic capacity (Ahmadi et al., 2010) . However, PI failed to use water sparingly on a canopy basis, as reported under a partial root zone drying irrigation strategy (Ahmadi et al., 2010), because of very high T soon after irrigation. 5.4.4 Leaf water potential (?w) Water deficit under rain- fed conditions decreased leaf water potential, as observed in the previous field experiment . Contrary to the previous year, Taewa and modern cultivars, which were exposed to same soil moisture , significantly differed in leaf water potential, possibly due to high drought intensity compared to the 2009/ 2010 growing season. Taewa, particularly Tutaekuri , were very tolerant, whilst Agria was very vulnerable to water stress. This difference demonstrates genotypic variability for the management of leaf water potential between Taewa and modern cultivar. Examination of the gaseous exchange behavi our in Taewa, compared to Agria ( as presented above) coupled with the leaf water potential results, supports Taewa?s superior photosynthetic capacity under water stress. Olesinski et al. (1989) reiterated that both leaf water potential and gaseous exchange parameters are influenced by irrigation frequency in potato. Regardless that gaseous exchange is more indicative of water stress ( Olesinski et al., 1989), this study shows that leaf water potential can also be used as an indicator for water stress and for irrigation guidance. L eaf water potential for FI and PI were not different in Taewa, but the two were different in Agria. The result suggests that Taewa, specifically Tutaekuri, can be scheduled at PI without more water stress, whereas Agria requires FI for the same leaf water potential with Taewa, under PI scheduling. CHAPTER FIVE Taewa and Agria response to irrigation and N 176 Figure 5. 13 Relationship between photosynthetic WUE (PWUE) and Ci (a) and between net photosynthesis (A n) and g s (b) in potato cultivars CHAPTER FIVE Taewa and Agria response to irrigation and N 177 5.4.5 Tuber yield and yield components Taewa yield response to irrigation and N was generally lower than the modern potato cultivar, Agria. For instance, Moe Moe and Agria tuber yield responded to FI, whilst Tutaekuri responded to PI. Both Tutaekuri and Moe Moe decreased total and marketable tuber yield with high N, whereas Agria increased total and marketable tuber yield with high N. The high N reduced tubers per plant, tuber weight and HI in Taewa, whilst increasing them in the modern cultivar, Agria. This indicates that, although N improves yields in irrigated potato more than in water- stressed fields ( Ferreira et al., 2007), the response to N depends on cultivars, as reported for Agria, Fianna, Russet Burbank, Ilam Hardy and Kennebec cultivars in New Zealand (Craighead et al., 2003) . Consequently, Craighead et al. ( 2003) recommended N application up to 210 - 250 kg ha- 1 as a suitable range for tuber yield response in New Zealand. Taewa growers do not need to apply the amount of N applied to modern potato cultivars. Irrigation enhances tuber yields through the modification of partitioning more assimilates to the tuber, depending on the cultivars (Belanger et al., 2001; Walworth et al., 2002) . In this study, FI moderately improved the number of tubers, HI and mean tuber weight in Agria and Moe Moe, whilst decreasing them in Tutaekuri. The tuber yield improvement with irrigation and N in Tutaekuri was greatly limited by genotypic potential. Consequently, the large tuber numbers per plant and small tuber size hampered Tutaekuri tuber yield. This supports documentation which describes S.andigena yields as primitive and limited by large above- ground biomass (Kumar et al., 2006) . Nevertheless, the current study indicate s the possibility of achieving higher tuber yields in Tutaekuri, with PI and low N . This study has also confirmed the previous failure of FI to improve Tutaekuri tuber yield, in a glasshouse (Chapter 3) and in the field ( Chapter 4) . In this study, Agria demonst rated high yield potential compared to the Taewa cultivars. Moe Moe did not compet e well with Agria, compared to the glasshouse and 2010 field experiments. The relative low yields of Moe Moe in this study are most likely to have been the result of potato psyllid infestation ( Bactericera cockerelli ), during the late stages of the crop. Visual surveillance showed potato psyllid symptoms 1 10 - 150 days after planting ( Fig. 7.1). The attack had less impact on Agria yield, since it had already developed tubers, whilst Taewa was still developing tubers when infested: hence, CHAPTER FIVE Taewa and Agria response to irrigation and N 178 Taewa yields were probably decreased due to the pest?s disruption of the photosynthesi s and tuber dry matter accumulation process. On the other hand, the performance of irrigated Moe Moe still contradicts statements that Taewa cultivars are 50% poorer in their tuber yields, compared to modern cultivars (Harris et al., 1999) . This study is illustrative of the claim that the low tuber yields commonly reported for Taewa may be at least partly due to pests and diseases and soil water management. However, these tuber yields are considerably above the current mean total and marketable tuber yields attained by Taewa growers, ranging from 15 - 20 t ha - 1 and 10 - 15 t ha- 1 , r espectively (Roskruge, 2011 pers. comm.) . Irrigation contributed to improvement in the tuber yield of Taewa, although this w as restrained by potato psyllid. Full irrigation and PI, respectively, raised Moe Moe and Tutaekuri tuber yields towards a potential yield of 40 t ha - 1 . 5.4.6 Water use efficiency, economic water productivity and nitrogen use efficiency The average WUE varied with cultivar, irrigation and N regimes , ranging from 4.5 kg m - 3 (Tutaekuri) to 12.4 kg m - 3 (Agria) among st cultivars; 7.0 kg m - 3 (FI) to 8.0 (PI) among st irrigation; and 7.0 kg m - 3 (high N) to 8.3 kg m - 3 (low N) among st N regimes, respectively. The WUE among st cultivars compares to 8 l/100g, 16.4 l /100g and 22 l /100g virtual water content for Agria, Moe Moe and Tutaekuri, respectively. This is lower than the estimate of mean global virtual water content of 25 l /100 g potato tuber (Hoekstra et al., 2007). Agria was more efficient in water use than the mean global WUE of 6.2 - 11.6 kg m - 3 (FAO, 2009), whilst Moe Moe , under low N, was within this range. T utaekuri was less than 6.2 kg m - 3 , except when partially irrigated and subject ed to low N treatments . The mean WUE for Taewa is below the range reported by FAO ( 2008, 2009), due to the impact of potato psyllid infection and high N on tuber yield. Nevertheless, furrow and drip irrigation studies for modern potato have also reported WUE within Taewa?s low range of 2.6 - 7.5 kg m 3 (Erdem et al., 2006) . Partial irrigation was a significant water saving strategy, through the lowering of actual ET below full water supply, whilst keeping a tuber yield that approached the tuber yield of FI . This helped PI to achieve high WUE and EWP without a much decline in tuber CHAPTER FIVE Taewa and Agria response to irrigation and N 179 yield and quality . The EWP for the three water regimes was 11.40 US$/m 3 (FI), 13.26 US$/m 3 (PI) and 12.25 US$/m 3 (P e). The EWP realised from this study are higher than 0.3 US$/m 3 reported in Jordan for potato tuber yield (FAO, 2003; Molden et al., 2001) . It is probable that the variations in EWP and WUE can be attributed to management, climate, market price and genotypes. This study has shown that PI had both physical and economical water saving attributes. The use of high WUE potato cultivars , high market value cultivars, moderate N and appropriate irrigation scheduling, facilitates the maximisation of crop water productivity (Wallace, 2000; Morison et al ., 200 7 ) . Cultivars and N consistently influenced WUE and NUE differently within the various water regimes (Battilani et al., 2004; Zebarth et al., 2008) . In this study, WUE and NUE were highest in Agria at high N and low N, respectively. The low N that limited WUE in Agria improved WUE in Taewa. H igh N led to both low NUE and WUE in Taewa . Similarly, PI had high WUE in Agria at high N , whilst it h ad deteriorating NUE . The FI that increased NUE in Agria and Moe Moe reduced its WUE. This finding supports several studies of modern production systems that have reported an increase in NUE with adequate water, whilst decreasing WUE (and vice versa) and that WUE is high where water is limited (Battilani et al., 2004) . However, WUE in Taewa w as influenced more by N than by irrigation scheduling. Generally , more water and N increase tuber yield of modern cultivars, whilst Taewa (especially Tutaekuri) requires lower quantities of water and N for high er productivity. This response suggests that Taewa and modern potato cultivars have different appropriate irrigation and N levels for efficient resource use. Therefore, growers should take into account the potato genotypic response to water and N for efficient water use. 5.4.7 Irrigation water use efficiency The tuber yield - water relationship for both Taewa and modern potato was linear, as also documented in most modern potato experiments (Ferreira et al., 2007). However, the tuber yield increase with irrigation was low in Taewa compared to the modern cultivar. Irrigation water use efficiency for Agria and Moe Moe was within the range ( 5.2 - 9.1 kg m- 3 ) reported by Ferreira et al. (2007), in a hot dry environment, but Agria was above IWUE for New Zealand (Hedley et al., 2009b) . In New Zealand, the IWUE for unifo rm and variable rate irrigation are 5.8 and 6.8 kg m - 3 (Hedley et al., 2009b). The IWUE for Moe Moe was within this range. Tutaekuri had lower IWU E than what h as previously been reported in a temperate and hot dry environment. In contrast to Ferreira et al. ( 2007) , CHAPTER FIVE Taewa and Agria response to irrigation and N 180 N had no influence on IWUE. In spite of high IWUE in modern cultivars, the yield reduction with water deficit indicates that it is more vulnerable to water stress compared to Moe Moe and Tutaekuri. Moe Moe is reliable for both irrigated and rain - fed conditions, whilst Agria is only reliable under full irrigation. 5.4.8 Specific gravity and tuber dry matter content Specific gravity and DM are more strongly influenced by cultivar (J efferies et al., 1993b) than irrigation and N (B?langer et al., 2002) . Taewa cultivars are high in DM and SG compared to Agria, thus indicating great tuber quality. The SG range in Taewa ( particularly Tutaekuri) was within the normal SG range of 1.055 to 1.09 50 (Kellock et al., 2004) , unlike the previous year (see Chapter 4, Section 4.3.1) and the glasshouse results (Chapter 3), which were above these values. Nevertheless, SG and DM for Tutaekuri demonstrated Singh ?s (2008) and Chapters 3 and 4 findings that SG and DM in Taewa are high compared to modern cultivars. Genetic factors and the late maturity of Taewa enhanced the accumulation of DM (Werner et al., 1998) . It is probable that psyllid infestation disrupted the DM accumulation process in Taewa, thus resulting in lower DM and SG than previous years as once reported in modern potato by Teulon et al., ( 2009) . Tutaekuri had the highest predicted starch concentration followed by Moe Moe and then Agria. Specific gravity and DM are positively related to starch , but negatively related to sugar concentration (Iritani et al., 1976) . This means that Agria had a high concentration of total sugars, as determined in Chapter 4 (see Section 4.3.1). For instance, reduced sugars and DM are usual benchmarks for processing potato quality assessment (Marquez et al., 1986) . The low DM in Agria would reduce productivity of the processed product and the amount of oil used for processed products, compared to Taewa ( Kellock et al., 2004). This implies that Taewa can produce more pr ocessed products with less oil, compared to modern cultivar , Agria . CHAPTER FIVE Taewa and Agria response to irrigation and N 181 5.4.9 Nitrogen concentration and potential N loss in the soil water The concentration of ammonium- N in the soil water was found to be greater than the concentration of nitrate- N but there was no difference in N loss between treatments . This study does not show that irrigation of potato necessarily results in high N leaching (Francis et al., 2003; MAF, 2002) . The possibility of nitrate leaching into the groundwater was not noticed in high N application or autumn season. The possible reason is that the N rate in this study is lower than 400 kg N ha - 1 applied by most growers in New Zealand (Martin et al., 2001) . This result suggests that low N practices can provide an acceptable nitrate leaching measure for Taewa growers. 5.5 Conclusion The effect of irrigation and N on vegetative growth, dry matter partitioning, photosynthetic WUE , DM and SG characteristics, N leaching , tuber yield, WUE and N UE in Taewa, were compared with the modern cultivar, Agria , in the field. Under FI , 92% of the 611 mm potential water requirement was supplied, whilst rain - fed supplied 60% and PI met 73%. Taewa used more water than Agria. Taewa grew wide bushes with tall main stems with multiple branches and large numbers of small tubers per plant, whilst the modern cultivar had a high number of short stems. The total dry matter production for Taewa and modern potatoes were the same, except that modern potato partitioned more to tubers, whereas Tae wa allocated more assimilates to tubers to the shoots and roots. Photosynthetic WUE and An differed with cultivars, irrigation and N , with the highest photosynthetic WUE and An in Taewa. Taewa achieved high photosynthetic WUE and An by maintaining high gs at low Ci compared to Agria. Taewa and modern potato differed in gaseous exchange, in the course of stomata conductance and because of growth stage differences. Full irrigation and N increased photosynthetic WUE and A n.. In addition, Taewa was very tolerant to water stress, whilst Agria was very vulnerable to water stress. This point is illustrated by the leaf water potential results. The characteristics of photosynthetic WUE and leaf water potential for Taewa offers a great physiological ability for drought adaptation, compared to the modern cultivar. It was also observed that Taewa had high DM and SG, compared to modern potato cultivars . It can be concluded that, in relation to physiological characteristics , Taewa has high CHAPTER FIVE Taewa and Agria response to irrigation and N 182 vegetative growth, photosyntheti c WUE, DM and SG, compared to modern potato cultivars. However, the modern cultivar was excellent in partitioning to tuber dry matter and early maturity. Taewa tuber yield, WUE, EWP and NUE are more sensitive to high N than the modern cultivar, Agria. However, Agria is more responsive to water stress than Taewa and therefore, Taewa require a low N in combination with PI, especially Tutaekuri, whereas Moe Moe requires a low N in combination with FI. Agria requires high N in combination with FI. Moe M oe indicates that it has the potential to compete with modern cultivar, if appropriate pest and disease management is put in place. The high EWP in Moe Moe may allow growers to economically and physically optimise their water resource use. It is suggest ed that Tutaekuri and Moe Moe also differ in some of their morphological and physiological characteristics. Tutaekuri has few er stems with more branches, many small tubers and larger stems and a higher shoot: root ratio than Moe Moe. On the other hand, the tube r yield, HI, WUE, EWP and NUE for Tutaekuri are smaller than that for Moe Moe. Tutaekuri responded to PI and it had low PR% , whilst Moe Moe performed well under FI . Both Tutaekuri and Moe Moe required very low N , and, therefore, it can be concluded that genotypic variation is high within Taewa and between Taewa and modern potatoes. CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 183 CHAPTER 6 EFFECT OF MECHANICAL AND HORMONAL CANOPY MANIPULATION ON TAEWA UNDER LIMITED AND UNLIMITED WATER AND NITROGEN CONDITIONS 6.1 Introduction Tutaekuri , also known as Urenika ( Solanum tuberosum ssp. andigena) is a distinctive Taewa or Maori potato cultivar (Harris, 2001). It is the most widely cultivated Taewa in New Zealand . The tubers are elongated with a dark purple skin and they have a very flourly flesh which fragments when boiled. The morphology of the Tutaekuri plant also exhibits the distinguishing features of undeveloped potato cultivars: long stolons, very deep eyes and late tuberisation. Harris (2001) described Tutaekuri as one of the Taewa cultivars still exhibiting the true ancestral characteristics of the Andean potato es. Tutaekuri has also been characterised by a large shoot biomass, many branches, many small tubers per plant and insensitivity to full irrigation compared to modern potato cultivars ( Chapters 4 and 5) . Tutaekuri is also known to possess high antioxidant activity (Lister, 2001 ) , high tuber dry matter content and specific gravity (Singh et al., 2008) ( Chapters 3 & 4 ) . However, it is handicapped by small tuber size and low yields like in other Andigena spp (Kumar et al., 2006) . High above- ground biomass suggests that Tutaekuri has the potential for yield improvement, through the manipulation of its shoot biomass and number of tubers. It was hypothesised that Tutaekuri utilizes a greater proportion of assimilates for above- ground dry matter production, rather than for tubers. Subsequent reduction of the leaf canopy, either by application of growth regulatory hormones or mechanical control, would stimulate increased allocation of assimilates to tubers. Tutaekuri appears to strongly favour the source of assimilate (shoots) over the below - ground sinks (tubers). The results of an earlier experiment show high photosynthetic capacity and LAI, accompanied with low tuber yield, in Tutaekuri ( Chapters 3, 4 and 5) . Consequently, above - ground dry matter production was greater than the tuber dry CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 184 matter production. Gifford et al. (198 1) indicated that plants with sinks, which strive effectively for assimilates, experience reduced vegetative growth, due to heavy tuberisation. However, it is not known whether the above - ground sink size actually control partitioning to the below- ground sink in Tutaekuri. Physical alteration of a large leaf canopy reduces water use, whilst increasing yield in potato (Hossain et al., 19 92), wheat (Richards, 19 83) and temperate pasture (John et al., 1973) . Numerous studies have also established that the application of chlorocholine chloride (CCC) enhances tuberisation in Solanum tuberosum ( Wang et al., 2010a ) and Solanum tuberosum ssp. andigena (Kumar et al., 1974) . Mechanical topping and CCC reduce competition between the canopy and tubers for assimilates. Chlorocholine chloride impedes vegetative growth in potato crops by hindering gibberellin, but improving tuberisation and photosynthetic capacity (Wang et al., 2010) . Nevertheless, there have not been any leaf canopy modification studies on Taewa cultivars in New Zealand, in order to characterise the effects of mechanical topping and CCC spray schedules on the partitioning of photoassimilates between the source and the sink, under field conditions. This field experiment examined the consequences of mechanical canopy topping and CCC foliar application on dry matter partitioning, tuber yield and water use efficiency in the Taewa cultivar, Tutaekuri ( Solanum tuberosum ssp. andigena), under limited and unlimited water and nitrogen environments. The purpose for this study was to improve the yield and WUE of Taewa cultivar, Tutaekuri. 6.2 Material and Methods 6.2.1 Experimental Site The field experiment was conducted at the Pasture and Crop Research Uni t, Massey University , Palmerston North , New Zealand. It was planted on 27 th October 2010 and harvested on 15 th April, 2011. The soil and weather for site have been presented in Table 5.1 and Figure 5.2 ( See Chapter 5 ) . CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 185 6.2.2 Experimental design and crop management 6.2.2.1 Treatments and experimental design The field experiment was a Randomised Complete Block Split - Split - plot Design (RCBD Split- Split- plot) with two water regimes as the main treatments (rain - fed and full irrigation); four canopy manipula tions as sub- treatments; and two fertiliser rates (N1=0 and N2=140 kg ha - 1 ) as sub - sub- treatments. This was replicated four times (Fig. 6.1). Both fertiliser treatments received PK as a basal dressing and N was applied as a side dressing of urea. 6.2.2.2 L eaf canopy manipulation treatments The four canopy manipulation treatments were as follows: (1) normal growth as a control (NGC); (2) application of CCC ( 2- chloroethyltrimethyl- ammonium chloride, at 2 g l - 1 (2000 ppm), twice during the tuber initiation stage at 25 and 30 days after plant emergence (DAE), coded as 25 - 30 CCC ( Wang et al., 2009a ) ; (3 ) application of CCC at 2 g l - 1 (2000 ppm) twice during the tuber initiation stage at 25 and 50 DAE , coded as 25- 50 CCC; and (4) mechanical canopy topping. M echanical canopy topping was implemented by cutting the shoots on top of the potato bush by one third of the plant (Plate 6.1). A manual hedge shear with heavy duty precision cutting blades was used for topping the canopy 52 DAE on 7 th January, 2011. Chlorocholine chloride was applied (from cycocel 750 brand manufactured by OHP, INC .) using a backpack sprayer at 350 litres of water per hectare. Both CCC treatments received an initial treatment on 12 th December, 2010. The second application for the 25- 30 CCC treatment was applied on 17 th December, 2010. T he second application for the 25- 50 CCC treatment was applied on 3 rd January, 2011. 6.2.2.3 Irrigation and fertiliser application The irrigation treatment received 25 mm irrigation at 30 mm soil moisture deficit (SMD), between 4 th December, 2010 and 20 th March, 2011. Irrigation was applied by Trail boom traveller irrigator. Crop water use, for irrigated and rain- fed treatments, was determined by the soil water balance approach ( see Chapter 4) . All plots received 30 kg P and 75 kg K ha - 1 (at planting) of Potash Super 30% fertiliser (0- 6 - 15- 8) applied at 500 CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 186 kg ha - 1 . The crop on NPK fertiliser treatment received 140 kg N ha - 1 from urea (as a side dressing), whilst the other crop did not have a pplied. Nitrogen fertiliser was applied on 10 th December, 2010, 24 DAE . This was followed by mounding on the same day. All other field husbandry practices (i.e. weeding and plant protection) were carried out, as previously described in Chapter 5. 6.2.3 Plot-size and plant spacing Potato tubers were manually planted on 27 th October, 2010, at 75 cm spacing between rows and 30 cm spacing within rows, at a depth of 10 - 15 cm. Each plot was 3 m by 1.5 m, containing 18 plants and was bordered by two guard rows planted with the same potato cultivar (Fig. 6.1). 6.2.4 Plant physiological characteristics and biomass partitioning measurements Gaseous exchange was measured once on 23 rd February, 2011 (120 DAE ), by using a CIRAS - 2 Portable Photosynthesis System ( V2.01 ) , in order to determine leaf stomata conductance (m molCO 2 m 2 s- 1 ) ; net photosynthesis ( ?mol CO 2 m 2 s- 1 ); transpiration rate (m molH 2 O m 2 s- 1 ) and internal Co2 concentration (ppm), detailed in Chapters 3 and 4. The above- ground (leaves and stems) and below - ground biomass (roots and tubers) were sampled on 28 th February 2011, 125 DAE to determine the effect of leaf canopy manipulation on partitioning of dry matter to leaves, stems, ro ots or stolons and tubers. One small and one large plant sample was randomly uprooted from each plot using a spade. They were partitioned into leaves, stems, roots and tubers and then weighed and oven dried at 70 oC, until there was further weight loss . The contribution of each component to total biomass on dry matter basis was determined as the ratio of each partition to total biomass (leaves, stems, roots and tubers); per plant (Geremew et al., 2007) . The HI was calculated as the ratio of total tuber dry matter to total biomass on dry matter basis from the samples of each plot (Mackerron et al., 1985) . Leaf area, plant height (cm) and number of stems and their diameter (mm) were measured at physiological maturity. Potato psyllid were visually scored on a scale of 0 - 5, with 0 representing no infection and 5 being the highest infections, per experimental unit, on 14 th March, 2011 (Puketapu, 2010; Roskruge et al., 2010) . Leaf area was determined using a leaf area meter. Volumetric soil moisture was monitored using a TDR, model 1502C, Tektronix Inc., Beaverton, OR, USA) , described in previous chapters. CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 187 Figure 6. 1 Schematic diagram for Field Experiment 4 on canopy manipulation CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 188 6.2.5 Potato tuber yield and statistical analyses Data on plant height , number of stems and branches per plant and their diameter (mm) , leaf area, number of tubers per plant, mean tuber weight and total tuber weight, marketable tuber yield and tuber dry matter content, were measured at harvest. These data and those on the physiological characteristics were analysed with the GLM procedure of the S AS (SAS, 2008) ; differences amongst treatment means were compared by the LSD , at the 5% probability level (Meier, 2006) . The RCBD Split- Split- plot linear statistical model used in GLM procedure was as follows: ?ijk = ? + ? i+? j +(??)ij +? k +(??)ik +(??) j k +(???)ijk +?ijk ; Where, ? is the overall mean; ? i , ? j , (??)ij represents the whole plot as water regimes, block and whole plot error effects; ? k , (??)ik , (??) j k represents subplots, as canopy manipulation effects, block effects and subplot errors; (???)ijk represents whole plot and subplot interaction effects; and ?ijk represents overall error, respectively, whilst i= 1 - 2 water regimes, j=1 - 4 replicates and k=1 - 4 canopy manipulations. Plate 6. 1 : Mechanical canopy topping in Tutaekuri, Solanum tuberosum ssp. andigena in 2010/ 2011 (a) Mechanical canopy topping (b)Size of shoots topped CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 189 6.3. Results 6.3.1 Evapotranspiration of Tutaekuri The Tutaekuri growing season was 170 days, with a potential crop water requirement of 590 mm (Table 6.1). A seasonal precipitation of 368 mm contributed 63% of the total crop water requirement. Consequently, the potential crop water requirement, to be met by irrigation was 278 mm. The ratio of actual water use over potential evapotranspiration per crop stage indicated water stress in the rain- fed treatment, at the vegetative (64% ) , development (52%) and mid- stages (65%), whilst the establishment and maturity stages (90 %) had the same water use as seen in irrigated treatments (Table 6.6). Table 6. 1 Potential crop evapotranspiration (ETp), precipitation (P e), irrigation (I), deep percolation (D p), soil moisture change (?S), actual evapotranspiration ( ETc) [ETc = Pe + I ? Dp + ?S ] in mm, per crop stage of a Taewa cultivar, Tutaekuri The actual water use varied with canopy manipulation (P<0.01) and water regime treatments (P<0.0001), but not between N treatments (P>0.05, Table 6.6 ). The mean actual water use for irrigation was 5490 (m 3 ha- 1 ), whilst rain - fed used 38 30 (m 3 ha- 1 ). Amongst the canopy manipulation treatments, the mechanical topping had the highest water use, although it was not different from the 25- 30CCC schedule, which was not different from the 25- 50CCC schedule. The control used the least amount of water, although it was not different from the 25- 50CCC schedule (P>0.05, Table 6.6). CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 190 6.3.2 Volumetric soil moisture (%) Figure 6. 2 Change in volumetric soil moisture (%) during the growing season in Tutaekuri, 2010/ 2011. Error bar represents ?SEM. Volumetric soil moisture content (%) was significantly influenced by water regime (P<0.0001) and days after planting (DAP) (P<0.0001, Fig. 6.2 ). Irrigation increased the volumetric soil moisture content (P<0.05), but N and canopy manipulation had no much effect on soil moisture content (P>0.05). Significant interactions with soil moisture were observed between water regime*DAP (P<0.001, Fig. 6.2) . Figure 6.2 shows that the interaction in soil moisture, between DAP and water regimes, was a result of differences in water inputs on different days. The greatest depletion in soil moisture was from Days 60 to 120 after planting, in both irrigated and rai n- fed. However, rain - fed had the lowest soil moisture. The days of water deficits correspond to the vegetative, development and mid- stages shown in Table 6.1, when the rain- fed crop was greatly water stressed. Drought during this period decreased soil moisture in both irrigated and rain- fed treatments. CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 191 6.3.3 Photosynthetic water use efficiency and gaseous exchange G aseous exchange was significantly affected by water and N regimes (P<0.05 ; Table 6.2), but not by canopy manipulations (P>0.05). Irrigation significantly increased net photosynthesis (A n) (P <0.0001), stomatal conductance (g s ) (P<0.0001) and transpiration rate (T) ( P<0.001), whilst it reduced leaf temperature (LT) (P<0.01). Photosynthetic water use efficiency (photosyntheitic WUE), defined as the ratio of An to T, was not influenced by either water regime or canopy manipulations (P>0.05) , but it was influenced by N (P<0.05 ) . However, photosynthetic WUE was highest under irrigation, where the canopy was topped or sprayed with CCC at Days 25 to 30. Exclusion of N reduced photosynthetic WUE ( P<0.05) , A n, g s and T ( P<0.01) ( Table 6.2) . The relationship of photosynthetic WUE to A n, gs, T, LT and Ci, was explored, by using simple correlation. With all data combined, correlation between photosynthetic WUE and An (r = 0.78), g s (r = 0.45) and T (r = 0.51) were generally positive (P<0.0001). However, photosynthetic WUE negatively correlated with LT (r = - 0.65) and Ci (r = - 0.94) (Appendix 6.2) . CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 192 Table 6. 2 Effect of leaf area manipulation, water and nitrogen regimes on gaseous exchange in Taewa cultivar Tutaekuri CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 193 6.3.4 Vegetative plant growth characteristics Canopy manipulation significantly affected plant height (P< 0.0001), the number of branches per plant (P<0.01) and LAI (P<0.001) , but it did not affect the number of stems per plant, stem diameter and potato psyllid score (P>0.05; Table 6.3). Mechanical topping of the canopy significantly reduced plant height, whil st application of CCC on different days reduced it intermediately, compared to the control which had the greatest plant height (Table 6.3). However, mechanical topping increased the number of branches per plant, whilst the growth regulator reduced it. Both mechanical topping and the two CCC application schedules decreased LAI (Table 6.3). Table 6. 3 Effect of leaf area manipulation on vegetative plant growth characteristics in Tutaekuri at physiological maturity, 2010/ 2011 Water regimes influenced stem diameter (P<0.01) and potato psyllid (P<0.0001), but did not affect average plant height, number of stems, branches and LAI per plant (P>0.05; Table 6.3). Nitrogen increased plant height (P<0.0001), LAI (P<0.001) and potato psyllid (P<0.001), but it did not affect the average number of stems, branches and stem diameter per plant (P>0.05). Irrigation increased the stem diameter a nd incidences of potato psyllid, whereas N exclusion decreased plant height (P<0.0001), potato psyllid CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 194 incidences (P<0.001 ) and LAI (P<0.0001), compared to where N was applied (Table 6.3). Nitrogen did not affect the number of stems and branches per plant, or stem diameter. 6.3.5 Dry matter production and partitioning There were significant differences between canopy manipulation treatments in the partitioning of fresh and dry matter to the leaf (P<0.0001, P<0.01), stem (P<0.01, P<0.05), roots (Ns, P<0.05), tuber (P<0.0001, P<0.05) and total biomass (P<0.05, Ns), in addition to HI (P<0.0001, Table 6.4). Noticeably, partitioning to the roots did not differ on a fresh weight basis, whilst total biomass production per plant did not vary on a dry matter basis (P>0.05; Table 6.4). Application of CCC at two schedules and mechanical topping reduced leaf fresh and dry matter production, compared to the control. However, the greatest reduction was observed in the 25 - 50CCC schedule. The 25- 30CCC and 25- 50CCC treatments reduced stem fresh and dry matter production, the lowest being in 25 - 50CCC. Root dry matter production was significantly increased by mechanical topping (compared to the control) (P<0.05), although it was not different from 25 - 30CCC, which was also greater than the control and 25- 50CCC treatment. Tuber fresh and dry matter production per plant was strongly influenced by 25- 50CCC, 25- 30CCC and mechanical topping, compared to the control, which had the lowest tuber fresh or dry matter production (P<0.0001, P<0.05; Table 6.4). The effect of CCC application in enhancing tuber production, compared to above - ground biomass, was confirmed by the way in which the CCC application significantly increased HI compared to the control (P<0.0001), after 125 DAE (Table 6.4). The 25- 30CCC and 25- 50CCC treatment and the mechanical toppi ng affected HI similarly. The HI, under mechanical topping, was less than 25- 50CCC (P<0.0001), but greater than the control. CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 195 Table 6. 4 Effect of leaf area manipulation on dry matter production and partitioning per plant in Tutaekuri after 125 day emergence, 2011 CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 196 Irrigation enhanced tuber production (P<0.01) and total biomass production ( fresh and dry weight basis) (P<0.01) and fresh stem biomass production per plant 125 DAE (P<0.0001; Table 6.4). Conversely, water regime had no effect on leaf and root fresh or dry matter production, stem dry matter and HI (P> 0.05). There were also significant differences between complete exclusion of N application and application of N. Application of N extensively increased partitioning to the fresh and dry leaves (P<0.0001, P<0.05), stem (P<0.001, P<0.01) and total fresh biom ass production (P<0.001, Ns) , respectively and it significantly reduced HI (P<0.001). However, N had no effect on tuber and root fresh and dry matter production per plant (P>0.05). The 25- 50CCC schedule resulted in 58% of assimilates partitioned to the tuber, whilst 25- 30CCC and mechanical topping partitioned 48% of dry matter to the tubers. The control only allocated 26% to the tubers and the remainder to leaf (32%) , stem (24%) and roots (19%), after 12 5 days from planting. The addition of N decreased all ocation to the tubers by 32% (25 - 3 0CCC), 13% (25- 50CCC), 11% (mechanical topping) and 36% in the control. Exclusion of N in Tutaekuri production reduced partitioning of dry matter to the leaves and stem, whilst it increased tuber proportion (Table 6.4). 6.3.6 Tuber yield and yield components at final harvest Canopy manipulation strongly affected total tuber yield (P<0.0001) , marketable tuber yield (P<0.0001) , number of tubers per plant (P<0.05) , and final HI ( P<0.0001; Table 6.5). However, it did not affe ct mean tuber weight for total and marketable yield (P>0.05). The 25- 30CCC and 25- 50CCC schedules had the highest total tuber yield, with 25- 30CCC being greater than mechanical topping, but not 25- 50CCC (Table 6.5). Mechanical topping was intermediate for total tuber yield, although not different from 25- 50CCC. Marketable tuber yield and HI were not different between mechanical topping, 25- 30CCC and 25- 50CCC, with 25- 30CCC being greater than mechanical topping and 25- 50CCC. The control had the lowest total tuber yield (t ha - 1 ) , marketable tuber yield (t ha - 1 ) , number of tubers per plant, and final HI. Canopy management greatly improved marketable tuber yield by 3 2 - 44%, compared to 20 - 32.8% increase on total tuber yield (Table 6.5). Irrigation increased mean tuber weight (P<0.000 1) , total tuber yield (P<0.0001) , mean marketable tuber weight (P<0.01) , marketable tuber yield (P<0.001) and final HI CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 197 (P<0.0001), but did not affect the number of tubers per plant (P>0.05, Table 6.5). The mean tuber weight (g) , total tuber yield, mean marketable tuber weight (g) , marketable tuber yield and final HI, were increased by 43%, 52%, 19%, 74% and 23% with irrigation, respectively. On the contrary, N decreased the mean tuber weight (P<0.01) , total tuber yield (P<0.0001) , final HI at harvest (P<0.0001) , mean marketable tuber weight (P<0.01) and marketable tuber yield (P<0.0001). The number of tubers per plant was not influenced by N. N itrogen decreased the mean tuber weight (g) , total tuber yield, mean market tuber weight (g) , marketable tuber yield , and final HI by 30%, 27%, 19%, 19% and 41% , respectively. Table 6. 5 Average tuber per plant, mean tuber weight (g) , total and marketable tuber yield and final HI for Tutaekuri under different water and N regimes , 2010/ 2011 CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 198 There was a significant interaction between irrigation and canopy manipulation on total tuber yield (P<0.01, Fig. 6.3) and on mean marketable tuber weight (P<0.05). There was a rapid decrease in tuber yield for 25 - 50CCC, from t he highest under irrigation to the lowest under rain- fed conditions, amongst the three canopy manipulations, whereas the tuber yield decrease from mechanical topping and 25- 30CCC were constant and small. Mechanical topping and 25- 30CCC performed better tha n 25- 50CCC, under rain- fed (Fig. 6.3) Figure 6. 3 Interaction between water regimes and canopy manipulation on total yield. Error bar represents ?SE M. 6.3.7 Water use efficiency and irrigation water use efficiency Water use efficiency (Kg ha- 1 m- 3 ) determined as the ratio of total tuber yield (t ha - 1 ) to actual crop water use (m 3 ha- 1 ) reflected tuber yield and water use. It was highest in 25 - 30CCC, which was significantly higher than the control and mechanical topping (P< 0.0001) (Table 6.6). Mechanical topping was intermediate, but significantly different from the control and smaller than 25- 50CCC. The modification of canopy CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 199 through 25 - 30CCC, 25- 50CCC and mechanical topping, respectively, increased WUE by 30%, 23% and 18%, compared to the control (Table 6.6). W ater use efficiency was not significantly influenced by irrigation (P>0.05), but it was influenced by N (P<0.0001). Application of N, as a side dressing after 24 DAE, reduced WUE by 26%, compared to treatments without N (Table 6.6). There was an interaction between irrigation and canopy manipulation on WUE (P<0.05, Fig. 6.4). Mechanical topping and 25- 30CCC had similar WUE between irrigation and rain - fed treatments, whilst 25 - 50CCC decreased relatively more under rain- fed environment, thus resulting in the interaction for WUE, which reflected the total tuber yield trend (Fig. 6.4 ). Table 6. 6 Effect of canopy manip ulation on crop water use (CWU) ; water use efficiency (WUE); and irrigation water use efficiency (IWUE ) for Tutaekuri, 2011 M ean IWUE was 5.5 kg m - 3 (r 2 = 52% ) with all data combined. With data stratified by canopy manipulation, IW UE was greatest in 25- 50CCC and lowest in the control (Table 6.6). For data stratified by N treatment, IW UE decreased from 6.0 to 4.8 (kg m - 3 ) with N application (Table 6.6). CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 200 6.4 Discussion 6.4.1 Photosynthetic WUE and gaseous exchange The results for photosynthetic WUE and gaseous exchange indicate d greater stomatal resistance with water and N deficit, regardless of canopy manipulation. This wa s demonstrated by improvement in An, gs, and T with irrigation and N, whereas water stress and zero N decreased photosynthetic WUE, A n, gs, and T in Tutaekuri, as once reported by Olesinski et al. (1989). Water and N deficit effects on Tutaekuri were highly related to stomatal resistance, as a restricting factor to photosynthetic WUE. The stomatal resistance increased by 80% and 36% by rain - fed and N deficit, respectively. It is probable that Tutaekuri c losed stomata in order to avoid high transpiration under the rain- fed environment. Studies show that stomata l resistance increases in potato with water and N stress, due to reduced leaf area and increased abcisic acid from roots to leaves, as a means of enduring drought, as reported under partial root zone drying (Liu et al., 2006b) . However, the control of the stomatal aperture did not increase photosynthetic WUE, as is expected in many plants. The possible reason for this could be the additional negative impact of high leaf temperature on photosynthesis, because gaseous exchange is also controlled by climatic factors. High leaf temperature raises atmospheric vapour pressure deficits, which then induces stomatal resistance (Sinclair et al., 1984) . The implication of high water vapour gradient is leaf water deficits that result in a declining An and T rate (Bunce, 2003) . High leaf temperature brings about mesophyllic resistance to photosynthesis in potato (Wolf et al., 1990) . Mesophyll ic and stomatal activity, without affecting Ci, were also reported by Schapendonk et al. (198 9) as being affected by water and N stress. T he integration of stomatal and mesophyl conductance is reported to be caused by a progressive build- up in water stress that results in secondary restrictions to An in C3 and C4 plants (Flexas et al., 2002; Ripley et al., 2010) . It can be presumed from the results in this study that the water deficit during the study period was very critical to the non- irrigated crops. This result supports reports by Ahmadi et al. (2010) and by Liu et al. (2006a) that water deficit is a primary limitation to potato photosynthetic capacity. Contrary to studies by Wang et al. (2009b) and Jones (1972) , these results do not indicate supremacy in CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 201 photosynthetic capacity for plants treated with CCC and mechanical topping, as reported in potato and Brussel sprout, respectively. A possible reason is that the days of gaseous exchange measurements after treatment differ from reports in the literature. Consequently, the short - term photosynthetic capacity induced by canopy manipulation might have been missed. 6.4.2 Vegetative growth and dry matter production The application of CCC and mechanical topping improved the partitioning of dry matter assimilates to the tuber, compared to the control. A schedule of 25 - 50CCC managed to increase partitioning to the tuber by 38%, whilst 25 - 30CCC and mechanical topping, respectively, increased assimilation of dry matter to the tuber by 21% and 24%, after 125 DAE . Plants treated with CCC managed to assimilate more dry matter to the tuber than mechanical topping, by reducing LAI, plant height and number of branches. Apart from reducing excess plant height and LAI, mechanical topping concurrently increased the partitioning of dry matter to axiliary branches and stems, thereby partially reducing its allocation to tubers, compared to the level of CCC. These results agree with Jones (1972) on the effects of topping Brussel sprout and by Wang et al. (2010) and Radwan et al. (1971) on the effects of CCC application effect on potato vegetative grow th and dry matter partitioning. According to Gifford et al. (1981) and Marcelis (1996 ), t he distribution of dry matter in plants is regulated by the sink. In another study by Tekalign et al. (2005), it was also observed that stronger sinks, such as developed berries and fruits, out - compete the tuber sink in dry matter distribution. The current study suggests that various growing shoots in Taewa have powerful sinks that result in competition with the below - ground sinks and tubers, when regulating the partitioning of assimilates. Spraying of CCC on leaves and the mechanical topping of growing shoots enhances the redirection of dry matter assimilates, f rom the excessive growing shoots to the tubers. Topping or pruning also enhances the redistribution of assimilates in Brussel sprout (Jones, 1972) and tomato (Heuvelink, 1997) to major sinks, whilst topping in sweet potato reduces partitioning to the tubers (Mulungu et al., 2006) . Growth regulators, CCC (Wang et al., 2010) and paclobutrazol (Tekalign et al., 2004), discourage excessive vegetative growth in potato, by inhibiting gibberellic acid, whilst mechanical topping disturbs the LAI and growing CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 202 shoots. Consequently, the photoassimilates manufactured by the remaining green area increases roots dry matter, apart from increasing tuber dry matter in Tutaekuri, as observed in other Solanum tuberosum ssp. andigena ( Kumar et al., 1974). Canopy manipulation induced Tutaekuri to respond to irrigation, through increased stem size and partitioning of dry matter to roots and tubers. However, irrigation increased the incidences of potato psyllid, compared to rain- fed treatment. Irrigation and large vegetative growth increases soil moisture and relative humidity, thereby creating a desirable micro- climate environment for pests and disease incidence (Olanya et al., 2007) . A study by Olanya et al. (2010 ), on the effect of irrigation and potato varieties on disease incidence, also found that irrigation increases disease prevalence, depending on the irrigation schedule and potato resistances level. However, another study on irrigation effect on late blight diseases, by Olanya et al. (2007), did not find a significant influence from irrigation on diseases and pest prevalence. Nevertheless, this study has indicated the influence of irrigation on potato psyllid prevalence in Solanum tuberosum spp.andigena (Tutaekuri). It is probable that partial irrigation scheduling (see Chapter 5) can reduce the incidence of pests and disease prevalence in Solanum tuberosum spp.andigena (Tutaekuri), as reported by Olanya et al. (2010), where proper irrigation reduced late blight and pest incidence in potatoes. The dry matter allocation to leaves and stems increased with N application, as a side dressing, compared to when N was completely excluded. Nitrogen increased vegetative growth at the expense of tubers, resulting in low HI. It is known that N fertilisation increases above- ground dry matter accumulation and LAI in some Solanum tuberosum ssp. andigena, whilst it decreases NUE and HI (Zebarth et al., 2008) . Consequently, canopy manipulation minimised the N effect of dec reasing dry matter partitioning to the tuber, through the rearrangement of assimilate distribution to the tubers. However, a combination of N and canopy management is an ideal strategy for Tutaekuri optimum translocation of assimilates to tubers in Tutaekuri . 6.4.3 Total tuber yield and yield components The foliar application of CCC (at 2 g ? - 1 in two schedules of 25- 30CCC and 25- 50CCC) and the mechanical topping at 52 DAE increased total tuber yield, marketable tuber yield and HI, compared to the control. The 25- 30CCC, 25- 50CCC and canopy topping increased total tuber yield by 33%, 28 % and 20%, respectively. All canopy CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 203 manipulation treatments achieved high tuber yield, by increasing the number of tubers per plant and HI. The increase in the number of tubers agrees with Rex (1992), whilst the total and marketable tuber yield increase with CCC, in this report, is in contrast to that of Rex, (1992) . This study implies that obstruction of excessive shoot growth in Tutaekuri enhances photoassimilates partitioning into tubers, thereby boosting tuber growth ( Wang et al., 20 09a ) . This finding also agrees with Kumar et al. (1974) and Sharma et al. (1998), who reported that CCC promotes tuberisation by reducing the level of gibberellins, which are reported to inhibit tuber formation and which promote vegetative growth in Solanum tuberosum ssp. andigena. In another study, Wanga et al., (2010) establi shed that CCC (at 2 g? - 1 in 25- 30 schedules) increased tuber yield in potato, by improving its nutrition status. On the other hand, this study indicated that higher number of tubers per plant in modified crops than control did not affect tuber yield, which was never reported in referred studies. The high number of tubers per plant (without decreasing tuber yield and marketable tubers between canopy manipulation treatments) suggest that there was no competition between tubers and vegetative growth on dry matter distribution. This implies that canopy manipulation strengthened the dominant sink to demand more assimilates: and assimilates were almost equally distributed between the tubers. It also means that the number of tubers per plant were not a limiting factor to dry matter allocation to tubers, due to canopy manipulation. Studies on fruit load in tomato have indicated that an increase in fruit load decreases the fruit weight and total yield, as a result of competition between fruit for assimilates (Heuvelink, 1997) . The low tuber weight and tuber yield in the control, despite it having a low number of tubers per plant in this study, confirms that the number of tubers competed with the enormous above- ground biomass for assimilates, at the expense of the tuber weight. This result suggests that the technique to improve Tutaekuri HI with regulatory hormo nes and mechanical topping is the mechanism to improve Taewa yield components. Mechanical topping, physically reduced the area for assimilate distribution and it redirected the distribution of most assimilates to the tuber, in the same way as the growth regulator, CCC. However, mechanical topping of plant leaf bearing shoots enhanced prompt regrowth of branches, as survival strategies for the reduced LAI for photosynthesis. It is probable that the increas e of stem or branches dry matter, following mechanical topping, contributed to low HI, compared to the CCC application. On the CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 204 other hand, the induction of root assimilation above CCC treatments helped mechanical topping treatments to abstract enough water thereby equat ing tuber yield with CCC treatments. The weakness of mechanical topping may include exposure of the plant to diseases, due to wounds and the increased probability of plant lodging, due to multiple branching as well as determination of proper topping time and number of topping. Fungal spray , partial irrigation (see Chapter 5) and low N may reduce disease exposure in mechanically topped Taewa. Hossain et al. (1992) found that topping potato at 30+45 DAP, followed by 30+60 DAP, increased the number of leaves, total leaf area, number of branches, number of tubers and tuber weight and tuber yield (32 - 35 t ha - 1 ) . The crop in this study was topped at 52 DAE, which is closer to 30+60 DAP found in the Hossain study (1992), thus indicating that it will be necessary, in the near future, to assess the appropriate time for topping Tutaekuri ( Solanum tuberosum ssp. andigena). For th ese reasons, both hormonal and mechanical canopy managements are realistic, in order to increase total tuber yield and mark etable tuber in Taewa. However, mechanical topping is more convenient and sustainable for the majority of Maori growers, who tend to prefer more natural interventions over use of growth regulators; also, growth regulators are more expensive than mechanical topping. Previous chapters have demonstrated that Tutaekuri tuber yield does not respond to full irrigation. The present study suggests that canopy modification induced Tutaekuri to respond to full irrigation. This supports Kumar et al. (1973) who reported that tuberisation in Solanum tuberosum ssp. andigena is regulated by specific stimuli (short - days and grafting) at active growing shoot points . The CCC and mechanical topping de- activates the factors in Tutaekuri which make it not respond to full irrigation. It is probable that mechanical topping induces mechanical resistance for ethylene production from indole- 3- acetic acid (IAA) the same as CCC (Vreugdenhil, et al., 1989). Ethylene increases with stress and it counteracts gibberellin negative effects on tuber formation by facilitating other hormones on tuber formation (Vreugdenhil, et al., 1989). The role of irrigation and the exclusion of N were well incorporated with CCC and mechanical topping. Therefore, the increased tuber yield resulting from these treatments was a consequence of increased partitioning of assimilates to roots and tubers. This shows that Tutaekuri management can be based on an integration of canopy, irrigation and N CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 205 management. However, growers need to bear in mind how the influence of canopy manipulation, on total tuber yield and marketable tuber yield, can vary with water regime and N. The study has shown that the mean tuber yield for 25- 50CCC sporadically decreased with water stress under rain- fed condition, whereas the tuber yield decrease (following mechanical topping and 25- 30CCC treatments) were constant and minimal. The way in which tuber declined in 25- 50CCC with water stress caused the interaction relating to tuber yield. This suggests that 25- 50CCC is not as e ffective as mechanical topping and 25- 30CCC, under water stress. The 25- 50CCC schedule is recommended for irrigated conditions, whilst mechanical topping and 25- 30CCC suit both environments. A possible reason for this finding is that mechanical topping and 25- 30CCC induced root development, which helped both to extract more water and withstand water stress, compared to the control and 25- 50CCC . 6.4.4 Crop water use, WUE and irrigation water use efficiency Plants whose leaf canopies were modified consumed more water, whilst increasing WUE and IWU E during the growing season, compared to the control . The 25- 30CCC and mechanical topping treatments used more water, due to well - developed roots, upon which potato water uptake depends (Stallham et al., 2004) . The ratio of actual water use to potential evapotranspiration for canopy manipulation (76% ) illustrates low water use in the control (74% ). Similarly, rain - fed treatments (63 % ) indicate that the irrigated treatment (93 % ) maintained water consumption closer to potential evapotranspiration, which is regarded as critical for maximum yield in potato (Ferreira et al., 2007) . The failure of rainfall to meet Tutaekuri water requirement can be fully observed in the critical stages (vegetative, development and mid - stage), thus indicating at what time irrigation is greatly needed in Tutaekuri. Subsequently, plant water extraction was greatly influenced by water availability, rather than canopy manipulation. The mean WUE varied with canopy manipulation and it ranged from 4.4 (control) to 5.7 ( 25- 30CCC ). This is below the global WUE average for potato, which ranges from 6.2 kg m - 3 to 11.6 kg m - 3 (FAO , 2009). However, the l eaf modification improved WUE for irrigated Tutaekuri, especially with 25- 30CCC, compared to the control (Fig.6.4) . This schedule responded to WUE because it facilitated the partitioning of asssimilates to both roots and tuber dry matter, resulting in high WUE. On the other hand, the IWUE CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 206 was highest in 25 - 50CCC, due to low water abstraction in relation to its low root dry matter, which allowed it to use the extra unit of irrigation water efficiently, compared with 25- 30CCC and mechanical topping. However, all canopy management effectively increased WUE and IW UE in Tutaekuri. Figure 6. 4 Interaction between water regime and canopy manipulation on water use efficiency ( WUE ) (kg m - 3 ). Error bar represents ?SEM The behaviour of WUE in Tutaekuri between the two water regimes is surprising, because the literature reports high WUE with restricted irrigation (Battilani et al. 2004) and with N application (Darwish et al., 2006). Contrary to these findings, WUE between irrigation and rain- fed did not vary and WUE was highe st in treatments without N . Failure of Tutaekuri to optimise water under a restricted water environment indicates that Solanum tuberosum ssp. andigena is not very efficient in water and N use for tuber production, compared to S. tuberosum, due to its low yield potential (Kumar et al., 2006). Solanum tuberosum ssp. andigena has not been bred for high WUE and NUE (Zebarth et al., 2004; Zebarth et al., 2008) ; it was the CCC and canopy topping strategies that enhanced WUE and IWUE . W ater use efficiency and IWUE results confirm earlier observations that canopy manipulation induces yield and efficient water use in Tutaekuri through root development, apart from the reduced canopy for CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 207 transpiration and the re- allocation of more dry matter to tubers. The significance of canopy management is that it optimises crop water use, by minimising water loss and excess vegetative growth, whilst maximising plant water uptake an d tuber productivity in Tutaekuri. According to this study, selection of T utaekuri for HI improvement is highly recommended inorder to enhance Taewa productivity in New Zealand. 6.5 Conclusion The study has examined the consequences of mechanical topping and foliar application of growth regulator (at the rate of 2g? - 1 on 25 - 3 0CCC and 25- 50CCC schedules) and compared it with normal growth on tuber yield and WUE in Tutaekuri. The results indicate that both growth regulator schedules and mechanical topping reduced excessive vegetative growth, whilst increasing the translocation of dry matter to the tubers, compared to the control ? but with different mechanisms. The 25- 30CCC schedule redirected most of assimilates, which would be used for vegetative growth, to the roots and tubers, whereas mechanical topping increased both roots and tubers, whilst it increased stem or branches dry matter. The 25 - 50CCC schedule had the highest tuber dry matter per plant with intermediate root dry matter. Irrigation facilitated assimilation to tubers, whilst the addition of N reduced HI, due to increased and excessive vegetative growth. The results also indicate that irrigation and N are paramount for enhancing photosynthetic WUE and photosynthetic capacity, regardless of canopy manipulation. Finally, the results suggest that the management of canopy increases the total tuber yield, WUE, and IWUE due to the redistribution of dry matter to the tuber. However , the final tuber yield depended on how each canopy management prepared the plant to use water efficiently. The 25 - 30CCC and mechanical topping easily helped to adapt the plant to water stress, by partitioning more assimilates to the roots, whilst the 25 - 50CCC delayed root development, since the second treatment was applied late and hence, it made the crop very sensitive to water stress resulting into high IW UE . Therefore 25 - 50CCC would be the recommended strategy for irrigated conditions, whilst all the other treatments would suit both irrigated and rain- fed conditions. It is recommended that growers should be managing the canopy of Tutaekuri , in order to optimise crop water use and tuber productivity, in New Zealand . CHAPTER SIX Mechanical and hormonal canopy manipulation in Taewa 208 CHAPTER 7 General Discussion and Conclusion 209 CHAPTER 7 GENERAL DISCUSSION AND CONCLUSION 7.1 Introduction Taewa and other heritage crop cultivars (e.g. Kamokamo) are important for the cultural economy of New Zealand (McFarlane, 2007). Relative to modern cultivars, heritage crops offer high premiums for growers selling in a niche market. Nevertheless, their productivity is very low, due to a lack of information on crop agronomic performance in modern production systems (Harris et al., 1999; Hayward, 2002). Modern crop cultivars (s uch as modern potato and B uttercup squash) have been widely studied, including aspects of water and nutrient use (Craighead et al., 1999). It is known that modern crops lack some of the nutritive value, processing and agronomic attributes, which are present in heritage cultivars (Lister, 2001; Singh et al., 2008). The current increase in economic water scarcity (IWMI, 2000, 2002), alongside issues related to climate change in New Zealand, requires crops with premium prices and technologies with a high efficiency of resource use. Therefore, research is needed in the Asia and Pacific region (especially on potato and other crops), which focus on improving WUE through identifying crop cultivars with high WUE and management technique that lead to the greatest WUE (Pandey, 2008; Clothier et al., 2010). The literature review in Chapter 2 highlights that the strategies for improved WUE can minimise water costs and environmental degradation, whilst maximising yields in order to meet market need s, in addition to enhancing net farm income. However, Taewa and other heritage crop cultivars in New Zealand have n ot previously been thoroughly studied for their water and N use efficiencies. It wa s not scientifically known whether low yields in heritage cultivars are the result of inappropriate soil and water management, or rather simple genetics. The overall objective of this study was to compare crop performance and water use efficiency in heritage and modern cultivars in response to irrigation and N management. Therefore, the general hypothetical question was: ?What is the impact of water and N management on heritage crop cultivars compared to modern crop cultivars, in relation to crop growth pattern, yield, WUE or economic value per unit of water used?? F our experiments were conducted: one glasshouse and three field experiments . Oca ( Oxalis tuberosa) and pumpkin squash (Cucurbita spp.) were studied once, as a supplement to Taewa and modern potato, which were the main crop s studied (Chapter 4). CHAPTER 7 General Discussion and Conclusion 210 At the beginning of the study, two Taewa (Moe Moe and Tutaekuri) and two modern potato cultivars (Moonlight and Agria) were studied in the glasshouse , at two different levels of irrigation (60% ET and 100% ET) and N (50 and 200 kg N ha- 1 ) , between June and November 2009 (Chapter 3). The second experiment during 2009/ 201 0, studied the four potato cultivars used in the glasshouse study, heritage pumpkin (Kamokamo) and modern pumpkin squash (Buttercup squash) , in addition to two unnamed oca cultivars grown under rain- fed and full irrigation, in the field (Chapter 4). This was followed by two field experiments in 2010/ 2011: Irrigation and N management in two Taewa (Moe Moe and Tutaekuri) and Agria , which were compared at three different levels of irrigation and two N rates (Chapter 5) . The fourth experiment was undertaken to determine the effect of canopy manipulation on the Taewa cultivar, T utaekuri (Chapter 6). This chapter provides a general discussion on all the results in order to better the performance of Taewa and other heritage crop cultivars. 7.2 Water requirements for studied heritage and modern crops Chapters 4 and 5 ha ve shown that modern and heritage crops differ in their growth stages or maturity and also that water distribution with the growing period varies. G rowers need to understand the growing stages and related daily water use in order to improve WUE . The daily water use fluctuates within the growing season ( Appendix 7.1). The mean daily ET c for 2009/ 2010 and 201 0/ 2011, in this study, were 3.2 to 3.6 mm, with a maximum daily ET c of 6.6 to 7.7 mm in January, and a minimum daily ET c of 0.3 to 0.4 mm in November, respectively. The daily crop water use for potato was strongly influenced by solar radiation (P<0.0001 , r=0.45) and maximum temperatures (P<0.0001, r=0.52) , but to a lesser amount by wind (Ns, r=0.12) , according to the correlation analysis with ET c. The high temperature and solar radiation experienced in January and February (67 - 127 DAP) cause d the maximum ET c ( Appendix 7.1). This observation suggests that the water requirement for Tae wa is very critical within the months of January and February . The maximum daily ET c, in this study, is lower than the 12 - 13 mm day - 1 and higher than the 4 mm day - 1 reported on potato grown in Portugal (Ferreira et al., 2002) and India (Kashyap et al., 20 01) , respectively. On the other hand, the ET c, for this study are within the daily potential evapotranspiration range of 0 to 12 mm day - 1 from winter to summer throughout New Zealand, respectively (NIWA, 2009 ). Scotter et al. (2000) modeled potential evapotranspiration for Palmerston North to have a maximum of 4.2 CHAPTER 7 General Discussion and Conclusion 211 mm day- 1 and minimum of 0.7 mm day - 1 using 25 years of historical weather data whilst Tait et al. (2007) estimated the potential evapotranspiration for New Zealand and found rates to range from 0.6 to 4.5 mm day - 1 . The data for ET c validate the variability of maximum and minimum potential evapotranspiration between seasons in New Zealand. Taewa required 610 mm of water over 170 - 180 days , whereas modern potato require d 490 - 550 mm for 140 - 150 days . Kamokamo and Buttercup squash require d 442 mm over 110 days , whilst oca requi red 678 mm over 224 days. The irrigation management study (C hapter 5 ) suggests that rain- fed only provided approximately 60% , and partial irrigation provided approximately 75% of the water requirement for potato. Consequently, rain- fed conditions result in a greater reduction in crop yield than partially irrigated potatoes. Almost all the heritage cultivars studied ( Taewa, Kamokamo and oca) use more water than modern cultivars when water is available. Taewa adapts to water stress in time of deficit more than modern cultivars. However, heritage cultivars prioritise allocation of water resources to vegetative growth, compared to modern cultivars (Agria, Moonlight, Buttercup squash) which then optimise partitioning of assimilates to the harvestable products. This observation confirms part of the study hypothesis that heritage crop cultivars differ from modern crop cultivars in their ability to use water. 7.3 Morphological and physiological characteristics of Taewa 7.3.1 Vegetative growth characteristics and dry matter partitioning One of the most interesting finding s is that total dry matter production potential does not differ genetically between Taewa and modern cultivars ( Chapters 4 and 5) . However, Taewa and the modern potato differ in HI, due to the way in which each cultivar allocates assimilates to tubers. The results in Chapters 4 and 5 consistently show that Taewa plants are genetically broad and tall with a large leaf canopy, whilst the modern potato plants have a large number of shorter, smaller stems with fewer thick leaves. Taewa (especially Tutaekuri) has a high number of small tubers, whilst modern potato has a few but larger tubers per plant (Chapter s 4 and 5). Modern potatoes partition more dry matter to tubers (>60% ) , whilst Taewa only allocates <60% to tubers with the remainder going to shoots and roots. These findings corroborate the abundant vegetative growth features observed in old wheat (Ko? et al., 2003; Siddique et al., 1990a ) , soyabean (Frederick et al., 1991) and CHAPTER 7 General Discussion and Conclusion 212 oat (Ziska et al., 2007) , compared to their modern cultivars. The significance of this result is that it suggests that development of the Taewa HI is far from its maximum potential value. The HI for modern potatoes may have nearly reached its maximum potential, as reported for many arable crops ( Richards et al., 2002) . Consequently, there are more opportunities for Taewa to improve its WUE , through the manipulation of vegetative growth traits in its HI , than for modern potatoes. The results from the three experiments reported in Chapter 3, 4 and 5 reveal that the potato cultivar? s morphological characteristics had a considerable influence on its water and N resource use (Manochehr et al., 2009; van Loon, 1981) . Taewa increases root dry matter and shoot to root ratio with water stress, as observed in native Andean drought tolerant potato clones (Schafleitner et al., 2007), whilst N increases vegetative growth , depending on the cultivar (Chapters 3 and 5). Manochehr et al. (2009 ) reported that the excess vegetative growth caused by high N does not improve potato tuber yield, as also observed in Taewa. The general view of the effect of water and N reveal s that, apart from using more water, Taewa has mechanisms that adapt to partial water and N stress. Taewa?s large canopy is disadvantageous to tuber yield but it helps with weed competition. Furthermore , the large canopy increases relative humidity and shading, which can increase pests and diseases incidences, radiation capture and the lodging of plants (Olanya et al., 2007) . This finding thus promotes the idea that a focus on modification of the Taewa leaf canopy should be a priority, in order to improve its productivity. Chapter 6 confirms that canopy modification can create a desirable micro- climate, which can reduce disease incidences and, at the same time increase assimilation to tubers, rather than excess vegetative growth. 7.3.2 Photosynthetic WUE and photosynthesis The other finding in this study is that Taewa and modern potato vary in gaseous exchange, due to the way in which Ci manipulates stomatal aperture and also as a result of maturity differences. During the 2010/ 2011 study, both A n and T were significantly reduced, without affecting photosynthetic WUE with water stress. S tomatal conductance and An were positively correlated in all the study years, whilst An was negatively correlated to Ci. These observations demonstrate that, apart from stomatal closure, mesophyllic conductance is responsible for photosynthetic capacity variability in Taewa and modern potato. This finding is in agreement with Schapendonk et al. CHAPTER 7 General Discussion and Conclusion 213 (1989) , who investigated how water stress affected An in five potato cultivars in the glasshouse. They discovered that there was a genotypic variation in An under well watered and limited water conditions. However, the response to water deficit was primarily regulated by stomatal closure and secondly, by the mesophyllic activity three days later. In another study on photosynthesis and productivity between old and modern durum wheat, Koc et al. (2003) reported that photosynthesis is largely affected by mesophyllic conductance, rather than stomatal conductance. It can now be confirmed that the integration of stomatal and mesophyllic conductance, which restrains photosynthesis in other C3 plants (Flexas et al., 2002; Ripley et al., 2010) , also exist s in Taewa and modern potato. Photosynthetic WUE and photosynthesis ( An) in potato are substantially affected by leaf age (Vos et al., 19 87; Ghosh et al., 2000) , genotypes (Tekalign et al., 2005), irrigation (Ahmadi et al., 2010) and N ( Ghosh et al., 2000; Olesinski et al., 1989) . These influences were observed with a photosynthetic WUE and A n increase over time (from D ay 20 to 50) and then a decrease, regar dless of cultivar, irrigation and N. The photosynthetic WUE and A n change with irrigation, N and crop development, indicating that gaseous exchange is sensitive to water and N stress, and growth stage, in both Taewa and modern potato. Chapters 3 and 4 show that Taewa had an extended and high photosynthetic WUE and A n, due to delayed tuberisation. Taewa growers are, therefore, advised to avoid water stress during the vegetative and development stage associated with tuber formation, in order to enhance photosynthetic capacity that will result in quality tuber set and development. Taewa achieved equal or high photosynthetic WUE and A n on average, compared to modern cultivars, due to a superior performance under both well watered and water deficit conditions ( Table 3.3, Table 5.4 and Appendix 4.4.3). The higher An and low leaf water potential, under rain - fed, suggest Taewa?s tolerance to water stress. The result for leaf water potential in Chapter 5 clearly show s that partial irrigation in Taewa does not cause more water stress, as seen with the modern cultivar, Agria. In addition, Chapter 4 (Section 4.3.1) and Chapter 5 reveal a genotypic variation in root: shoot ratio, which is a mechanism of drought or heat tolerance in potato (Basu & Minhas, 1991), in addition to being an indicator for HI (Siddique et al., 1990b). Tutaekuri and Moe Moe?s superior root: shoot ratio under water stress confirms that they had more roots for water CHAPTER 7 General Discussion and Conclusion 214 uptake, than those in modern potatoes . Siddique et al. (1990b) reported high HI and WUE in modern wheat cultivars with low root dry matter and root: shoot ratio. Similary, this study found high HI in modern potato with low root: shoot ratio. The se findings show that photosynthetic WUE , An leaf water potential and root: shoot ratio are outstanding attributes of Taewa, in relation to water use. 7.3.3 Tuber dry matter and specific gravity Taewa has been found to have a high solid texture and minimum total sugar content, which are common traits for assessing potato tuber quality (Westerm ann et al., 1994) . The results on DM, SG and total sugars prove that Taewa has an excellent processing quality , compared to modern potatoes as formerly reported by Singh et al. (2008) between Taewa and Nadine. The high DM and low total sugar content (Chapter 4 , Section 4 .3.1) in Taewa contributes to FAO Asia and Pacific region potato research needs, as debated by Pandey, (2008 ). The high SG and DM observed in Taewa are a more suitable quality for high processing cost recovery, whilst the low sugar concentration is essential for processing colour quality in crisps (Dahlenburg et al., 1990 quoting Burton, 1978 and Smith, 1975). Belanger et al. (2002) and Dahlenburg et al. (199 0) found that the aforementioned tuber characteristics are substantially influenced by soil moisture, N and cultivars. This study shows the stability of higher DM and SG in Taewa , rather than the modern potato ( see Chapters 3 and 5) , thus confirming the substantial influence of genotypic variation, rather than the environmental effect. Consequently, Taewa can provide potential genetic resources for improvement in the processing quality of modern potatoes within the Asia and Pacific region. However, selection of Taewa for high tuber quality has a compromise on tuber yield, becaus e tuber yield is negatively linearly related to SG [tuber yield = - 98.8 (SG) +116.6] and DM [tuber yield = - 0.53 (DM %) +26.49 (Appendix 7.7). Generally, the morphological and physiological characteristics traits , in this study, suggest that high An in Taewa are responsible for high vegetative growth, whilst late maturity is responsible for high DM and SG . Unfortunately, Taewa ?s low efficacy in allocating accumulated dry matter to tubers resulted in low HI , compared to modern potato cultivars, despite it having an equal potential for total dry matter productivity. The photosynthetic WUE and vegetative growth results demonstrates that crop CHAPTER 7 General Discussion and Conclusion 215 improvement has failed to increase relative growth rate and relative leaf area in modern crops, which are the basis for assimilation ( despite increasing HI ) as reported by Gifford et al. ( 1981) . Consequently, low gaseous exchange is reported in modern potato cultivars, compared to Taewa and other old or wild cultivars (Ko? et al., 2003) . There are many opportunities to maximise WUE and niche market access , through Taewa, due to its exceptional processing quality attributes , high photosynthetic capacity and expandable HI . 7.4 Tuber yield and yield components for Taewa The average yields of 52.6 t ha - 1 for Moe Moe under irrigation, in 2009/ 2010, demonstrate that it can achieve above the average potato yield range of 45.3 - 50.2 t ha - 1 in New Zealand (FAO, 2009; McKenzie, 199 9) , if proper agronomic practices are implemented. This result is also within the average potato tuber yield range of 38 - 55.4 t ha- 1 , upon which most modern potatoes are accepted for release in New Zealand (Anderson et al., 2004; Genet et al., 1997; Genet et al., 2001) . In contrast, Tutaekuri yield potential appears to be lower than the average of Moe Moe and modern potato yields. Consequently, the tuber yield gap between the two Taewa is very wide and difficult to close through agronomic practices because it is dependent on genotypic variation ( Appendix 7.2). However, both Taewa tuber yields varied with season and N levels ( Appendix 7.2). The main driver of change in the average tuber yields between the experiments was the potato psyllid infestation, as explained below ( Section 7.4.3) . Compared with 2009/ 2010, Taewa production in 2010/ 2011 decreased, with an average tuber yield of 18.1 t ha - 1 (18.3 to 17.8 t ha- 1 ) in Moe Moe and 10.9 t ha - 1 (8.4 to 13.3 t ha- 1 ) , in Tutaekuri under irrigation and rain- fed environments, respectively ( Appendix 7.3) . At NZ$962/tonne, a loss of 10.9 to 18.1 t ha - 1 in Tutaekuri and Moe Moe means that Taewa growers can potentially loose NZ$1 0,485 to NZ$17,412 per ha , with a potato psyllid infestation. This result shows that one of the main limitations to tuber yield in Taewa is potato psyllid infestation, apart from the low yield potential amongst other Taewa cultivars. Pest and disease control are essential in Taewa, despite their hardiness and tolerance to some biotic and abiotic stresses, which have been developed through their self- selection (Roskruge et al., 2010). Therefore, Taewa growers are advised to strategise pest and disease management, in order to attain maximum yield s and to avoid tuber yield decrease between seasons (see Section 7.4.1) . CHAPTER 7 General Discussion and Conclusion 216 7.4.1 How can Taewa growers maximise water and tuber yield in a modern production system? 7.4.1.1 Water and N management for improving Taewa yield and yield components The research found that irrigation, N and cultivar can influence tuber yield and yield components of Taewa, through the use of different mechanisms, as observed in other studies (Ojala et al., 1990) . The study suggests that the irrigation and N management commonly employed for a modern potato production system is not at all suitable for all Taewa. Similarly, Taewa cultivars vary in their response to water, but they are similar in their response to N. This finding suggests that low yields in Taewa are partly due to inefficient agronomic practices, apart from genetics. Growers can maximi se Taewa tuber yields with proper water and N combinations . When water and N input interactions are properly managed in Taewa, their combined effect will maximis e tuber yield and yield components. This study, in addition to Hayward?s (200 2) study, has shown that high N reduces tuber yield in Taewa, in favour of excessive vegetative growth and photosynthetic WUE. The reason for this is that Taewa?s water and nutrient use efficiency relies on its morphological and physiological characteristics. Moreover, yield, WU E and NUE are also negatively affected by the external factors of pest and disease in fully irrigated Taewa. Pests disrupt water and N interaction from maximi sing the benefits from properly managed water and N. Taewa growers need to prevent excess N and ex ternal constraints on irrigated Taewa, because an incorrect amount of N and water reduce s yields and wastes irrigation, in addition to causing environmental pollution (Cooke, 1986) . Full irrigation and 80 kg N ha - 1 or partly less, are recommended for Moe Moe (Chapter 5) , whilst Tutaekuri can grow without N ( or with minimal N ) and partial irrigation. 7.4.1.2 Canopy management for improved yield in Taewa The poor performance of Tutaekuri in the glasshouse and field compelled a study to examine the consequences of leaf canopy manipulation on tuber yield and WUE , under a limited and unlimited water and N environment (Chapter 6). This study suggests that excessive vegetative growth is responsible for low tuber yields and WUE in Taewa, and that this occurrence can be reversed by the use of mechanical or growth regulator canopy manipulations. This finding confirms the hypothesis that Taewa translocates more assimilates to its above- ground biomass, at the expense of large tubers. I n CHAPTER 7 General Discussion and Conclusion 217 addition, studies by Wang et al. ( 2009a ) and Wang et al. ( 2010) , a lso agree that chlorocholine chloride (CCC) proportionally reduces potato plant height and aboveground dry matter, whilst enhancing tuber yield in potato. Chlorocholine chloride?s influence on potato tuberisation has also been reported by Sharma et al. (1998). It promotes tuberisation by reducing the level of gibberellins, which are reported to inhibit tuber formation and promote stolon and shoot growth in Solanum tuberosum ssp. andigena and Solanum tuberosum ( Kumar et al., 1974; Sharma et al., 1998) . The effectiveness and rate of the CCC depends on the environment and cultural management for the plant being treated. Wang et al., (2010 ) reported that a CCC concentration of 1.5 ? 2.0 gl? 1 increased mineral nutrition in potato leaves, which contributed to a higher tuber yield. Mechanical leaf topping is practiced on tobacco, tomato, sweet potato and Brussels sprout, in order to enhance the re- allocation of assimilates to a harvestable product (Hossain et al., 1992; Jones, 1971). T he topping of potato, at 30+45 and 30+60 days after planting, increased tuber yield by 67% and 92%, respectively (Hossain et al., 1992) . The topping of shoots in volunteer potato plants was reported to have reduced the number of tubers and tuber biomass (Williams et al., 2002). Jones (1971) reported that mechanical topping of Brussels sprout reduced leaf area, thus resulting in a high net assimilation rate and the redistribution of dry matter, which was allocated into sprout production. In contrast , topping sweet potato fresh vines and leaves resulted in reduced root tuber yield, whilst increasing the yield of fresh vines and leaves (Mulungu et al., 2006) . The results from Mulungu et al. (2006) and Williams et al. ( 2002) are contradictory , in relation to the effects of topping reported in this study ( Chapter 6), in addition to Brussels sprout by Jones (1971) and potato by Hossain et al. ( 1992) . The main possible reason for this contradiction is their potatoes were topped to ground level. However , the number of positive results (on the effects of canopy topping) outweighs the negative results. This study, therefore, suggest s that Taewa growers (in order to maximis e their yield and WUE ) spray with CCC at Day 25 and 50 for irrigated conditions, whilst spray with CCC at Day 25 and 30 and mechanical topping techniques at Day 52 would suit both irrigated and rain- fed conditions. CHAPTER 7 General Discussion and Conclusion 218 7.4.1.3 Controlling the impact of potato psyllid on Taewa yield Potato psyllid has been causing yield losses to various solanaceous crops (potato, tomato) in New Zealand since 2006 ( Teulon et al., 2009; Puketapu, 2010) . In this study, potato psyllid did not affect the 2009/ 2010 Taewa and modern potato crop, following the spraying of 600g/litre methamidophos (Metafort 60S L), an organo- phosphorus insecticide. However, a potato psyllid infestation was observed late (150 DAP) in the 2010/ 2011 season, following the spraying of Avid (a bamectin) and Confidor (imidacloprid) , as presented in appendix 7.3. T he results for 2010/ 2011 indicate that there was a great reduction in tuber yield and tuber quality ( SG and DM ) in Taewa potato, compared to 2009/ 2010, as also reported in modern potato by Teulon et al. 2009. The yield loss in Taewa (especially Moe Moe) was higher ( > 40%) than that in the modern potato cultivar, Agria (13 %). New Zealand?s national potato psyllid monitoring results indicate that the potato psyllid population in the Manaw atu region was not serious in 2009/ 2010, compared to 2010/ 2011 ( Fig 7.1 ) . It also indicates that the potato psyllid population was high (in this experiment) 150 days (14 - 28 th March) after planting in 2010/ 2011. This trend of potato psyllid outbreak sugge sts that the difference in potato psyllid impact between years is not due to the effectiveness of insecticides used, but instead it is due to the size of the potato psyllid population and the time of the outbreak. Agria, might have escaped the potato psyllid ordeal, due to its early tuberisation and maturity. The spraying of pesticides in 2010/ 2011 ( Appendix 7.3) did stop at the time the modern potato had reached physiological maturity, and this was the same time that the potato psyllid population in Manawatu peaked (Fig . 7.1 ). Potato psyllid disrupted dry matter accumulation, at the critical stage of Taewa?s tuber dry matter accumulation (Plate 5.3) . Hence, Taewa required extended spray ing, in order to avoid the impact of potato psyllid at the later stage. The extension of a potato psyllid protection programme has an economic implication on Taewa growers, because it suggests an extended crop protection period to 170 days . Taewa will need more labour and chemicals costs, than for modern potato, in the c ase of potato psyllid protection. Taewa may require 15 - 17 sprays at 10 days interval , whilst modern potato may only require only 8 - 10 sprays (Appendix 7.3) . CHAPTER 7 General Discussion and Conclusion 219 The observations on potato psyllid infestation in 2010/ 2011 ( and viral disease in the glasshouse experiment on Taewa) confirm part of the study hypothesis that Taewa yields fell short, primarily due to agronomic practices ( pest and disease infection) disparity, rather than susceptibility to pest and diseases conditioned genetics. Taewa growers need to take pest and disease control seriously , in order to attain high tuber yield, quality and tuber dry matter content. Figure 7.1 Average numbers of potato psyllids (PP), per trap monitored i n Manawatu region, during the 200 9/ 2010 and 2010/ 2011 growing season (Sourced from http://www.potatoesnz.co.nz/Overview/What - we- are- working - on/Psyllid - resources.htm), Potato New Zealand. 7.5 Key water use performance indicators Water use efficiency is one of the main indices for water use in New Zealand (Aqualinc, 2006; Ford et al., 2009 ) . This study has assessed the performance of heritage and modern crop cultivars, in addition to agronomic practices , using a drought sensitivity index (DII); yield reduction percentage (PR%); geometric yield mean (GM y ) (Ramirez - Valejo et al., 1998) ; crop water use efficiency (WUE) ( Howell, 2001) ; water footprint (WF) or virtual water content (VWC) ( Hoekstra et al., 2009) ; economic water CHAPTER 7 General Discussion and Conclusion 220 productivity (EWP) ( Barker et al., 2003; Molden et al., 2001) ; nitrogen use efficiency (NUE) (Zebarth et al., 2008 and irrigation water use efficiency (IWUE ) ( Howell, 2001) . The DII, GM and PR% investigated the cultivars? genotypic sensitivity to water or drought situations; crop water productivity and WF ; EWP investigated the physical and economic productivity of cultivars, at a given unit of water; and IWUE investigated the marginal increase in yield, per unit of irrigation, in heritage and modern cultivars. The water footprint was used to compare cultivars between crops, whilst specific WUE was used to compare cultivars within one crop. S everal indices were used so as to quantify the physical and economic effects of changing varieties, irrigation and N management. Marsh et al., ( 1998) recommended the use of s everal indicators because they offer a more accurate result, per factor. This study found that water use performance indicators for the heritage and modern potato, pumpkin squa sh and oca fit in three categories: 1) one set indicated more yield, per unit of water used; 2) one set indicated a high marginal yield return, per additional unit of irrigation; and 3) one set indicated a higher economic return per unit of water used. Pumpkin squash (especially, Kamokamo) had more yield, per unit of water used because of its highest yield potential and EWP . Moe Moe ha s the highest EWP among potatoes, mostly due to its greater market value. On the other hand, modern potatoes responds well to irrigation, compared to pumpkin squash and Tutaekuri , due to their high IWUE and sensitivity to water stress. The selection of a crop for limited water should be based on its high yield and low yield reduction with water stress, in addition to EWP and low water footprint (as noticed in Kamokamo and Moe Moe). The selection of a crop for irrigation optimisation should be based on high IWU E , as well as high EWP and high yield potential (as observed in Agria and Moonlight). The heritage crops studied are relatively insensitive to soil moisture stress, compared to modern crops ( especially modern potato) . For i nstance, the results in Chapter 4 demonstrate that some heritage cultivars do not need full irrigation, even when water is limited, due to their genetic makeup (as observed in Tutaekuri) , whilst others need irrigation, due to their late matu rity (as observed in oca). The water stress indicators mentioned in Chapter 4 and 5 support the morphological and physiological characteristics in heritage crops, which can withstand water deficits, compared to CHAPTER 7 General Discussion and Conclusion 221 modern potatoes. Nevertheless, irrigation is essential for quality improvement in heritage crops. Where water is scarcer in New Zealand, partial irrigation may be an option, in this case, irrigation could be applied during sensitive crop development stages, rather than using a scarce water resource over oca or Taewa?s entire and extended growing season. These results suggest that key WUE indicators can easily be applied in selecting heritage crop enterprises or shifting to profitable heritage crop enterprises basing on a combination of market premiums, physica l water productivity and water availability. 7.5.1 Water footprint of growing potato, oca and pumpkin squash The mean total water footprint for full irrigation and rain- fed ranged from 9 5 to 111 m3 tonne- 1 (modern potato); 110 - 220 m3 tonne- 1 (Taewa); 46 - 82 m3 tonne- 1 (pumpkin squash) and 261 - 335 m3 tonne- 1 (oca) in 200 9/ 2010 ( Chapter 4) . In 2010/ 2011 t he mean water footprint for water regimes ranged from 163 - 586 m 3 tonne- 1 (FI), 173 - 406 m3 tonne- 1 (PI) and 198 - 505 m3 tonne- 1 (rain - fed) , with the lowest being found in Agria and the highest in Tutaekuri ( Appendix 7.4 ). The water footprint of Taewa greatly increased in 2011, compared to 2010 , due to a potato psyllid infestation and differences in maturity. It was found that the water footprint was reduced by partial irrigation for Tutaekuri and by full irrigation for Moe Moe and Agria. In New Zealand, Hedley (2009a ) has reported that the water footprint of modern potato production is smaller than the water footprint of maize and pasture: with potato registering 308 m 3 tonne- 1 and 325 m 3 tonne- 1 ; maize registering 622 m 3 tonne- 1 and 654 m3 tonne- 1 ; and pasture registering 2651 m3 tonne- 1 and 2667 m 3 tonne- 1 , at varied rate irrigation and uniform rate irrigation, respectively. The total water footprint of growing potato, in the study by Hedley et al. (2009ab ) , was higher than those reported by Hoekstra (2003) and the water footprint for this study, except for Tutaekuri. The water footprint of growing potato with no psyllid infestation (in both Taewa and modern potato) , in 2009/2010 (C hapter 4), is lower than the global water footprint ( 160 m3 tonne- 1 ) of growing potato. In the case of potato with psyllid infestation in 2010/2011, only a well managed full irrigation regime of modern potato and Moe Moe , gave a water footprint approximating the global water footprint of 160 m3 tonne- 1 . Partial irrigation improved the water footprint of Tutaekuri. Partial irrigation reduced the water footprint, by lowering the water volume needed to produce potato per tonnage by 12.6% , whilst maximising tuber yield over that found in the rain - fed crops. CHAPTER 7 General Discussion and Conclusion 222 The water footprint indicator suggests there are numerous disparities, with global averages and within country or seasons, arising from irrigation management and methodological differences when estimating crop water use, climate variability, cultivars and pest and disease infestation (Kumar et al. 2007; Hoekstra et al., 2007). However, the water footprint for crops grown in New Zealand can be reduced through good management ( Mekonnen et al., 2010b). For instance, pumpkin squash ( especially Kamokamo ) had the lowest water footprint, compared to oca, potato, maize and pasture in New Zealand , and compared well with small water footprint crops such as sugar beet and sugarcane, at the global level (Gerbens - Leenesa et al., 2009a ). This observation suggests that some heritage crop cultivars can compare with ( or outperform) modern cultivars in relation to water footprint, when the crop husbandry is appropriate. 7.5.2 Water use efficiency and crop water production functions in Taewa 7.5.2.1 Water use efficiency benchmarks in Taewa This study found WUE in potato ranging from 3.3 to 12.4 kg m - 3 amongst cultivars and 5.8 to 11.2 kg m - 3 amongst water regimes (Chapter 4 & 5 ). Tuber yield and NUE declined with PI and rain - fed, whilst it enhanced WUE, compared to FI in Agria and Moe Moe. This corroborate s the findings of Martin et al. (2006) who reported that high WUE in pasture production (rye grass and white clover) in New Zealand are obtained with restricted irrigation; but this is at the cost of pasture production. Water use efficiency for potato is higher than the WUE of pasture which is benchmarked at 2.0 kg DM ha - 1 m- 3 with a range from 0.07 to 2 .1 kg DM ha - 1 m- 3 in New Zealand (Martin et al., 2006). In this study, Taewa and modern potato optimal WUE is benchmarked at 6.5 kg m - 3 for modern potato, 6.0 kg m - 3 for Moe Moe and 3.7 kg m - 3 for Tutaekuri , using the method of Martin et al. (2006) for benchmarking pasture production WUE ( Appendix . 7.5) . Amongst the world?s major food crops, potato has been reported to have a high WUE of 6.2 - 11.6 kg m - 3 , compared to cereal and legume grain crops ( Bowen, 2003; FAO, 2008; Thompson et al., 2003; Zhang et al., 200 5) . The WUE for modern potato and Moe Moe are within this range. W ater use efficiency for potato has been reported above 11.6 kg m - 3 , as also observed with some modern potato treatments in this study ( Ka ng et al., 2004; Trebejo et al., 1990) . Erde m et al. (2006) reported WUE for potatoes below 6.2 kg m - 3 , as observed in Tutaekuri. The reason for low WUE in Tutaekuri could be its genetics on small tuber size or high er tuber number and higher vegetative growth than CHAPTER 7 General Discussion and Conclusion 223 tuber yield. The WUE for Tutaekuri improved with the enhancement of HI as reported in grain WUE (Siddique et al., 1990a ) . The WUE for Tutaekuri is above WUE for the major crops of the world and therefore, may be a valuable crop when water is limited. 7.5.2.2 Irrigation water use efficienc y and water stress index in Taewa Irrigation needs to be well planned for tuber yield and water resources optimisation in Taewa and modern potato cultivars. This study indicates that partial irrigation is optimal for Tutaekuri , whereas full irrigation is optimal for Moe Moe and Agria , because that is where the IWUE and yield were maximised . A failure to decide on these irrigation schedules can lead to a risk of yield reduction by 28.1% in Tutaekuri and 34.1% and 32.9% in Moe Moe and Agria, respectively (Table 5.9). The IW U E results, in combination with high yield reduction and high GM in Agria , highlights that the modern cultivar is physiologically more able to transform water to tuber (when water is optimal) , compared to Taewa w ith its tolerance to water stress. Taewa exhibited high drought tolerance characteristics under water and N stress. This ability confirms the findings from the physiological characteristics that suggest heritage crops are well adapted to low water and N su pply, despite their low yield potential. Novel i rrigation technologies enhance WUE by reducing non - stomatal water loss whilst efficient water use crops enhance WUE by increasing ET - Yield slope . In New Zealand, Hedley et al. (2009b) evaluated the IWUE of variable rate irrigation (VR I) , compared to uniform rate irrigation (UR I) , on a range of soils at five sites using centre pivot irrigator on pasture, maize and potatoes . It was found that VR I enhanced IW UE at all sites with the highest IW UE being found in potato (5.6 vs 6.8 kg m - 3 ) , whereas maize (3.3 vs 3.7 kg m - 3 ) and pasture (3.3 vs 4.6 kg m - 3 ) were low (Hedley et al., 2009b) . Onder et al. (2005) investigated the IWUE of surface drip and sub- surface drip irrigation at full irrigation ( FI ) , 66% of FI and 33% of FI and non- irrigated, where they found that IWUE was enhanced by deficit irrigation and surface drip irrigation (9.3 to 25.4 kg m - 3 ) , whilst full irrigation and subsurface irrigation had the lowest IWUE (9.0 to 23.0 kg m - 3 ). In another study, Er dem et al. (2006) reported that IWUE values increased from furrow (5.8 to 8.6 kg m - 3 ) to drip irrigation (7.2 to 13.7 kg m - 3 ) ( Erdem et al., 2006) . Some IWUE results in this study are greater than those found in reports by Hedley et al. (2009b) and those cited previously, except from drip irrigation. The main cause for the CHAPTER 7 General Discussion and Conclusion 224 variation appears to be the cultivar, in addition to irrigation management effects. T he effect of cultivar on IW UE is greater than the effect of irrigation scheduling. Theref ore, Taewa growers are recommended to combine techniques that maximi se both consumptive water use and reduce run- off, in order to achieve high WUE ( English et al., 2003) . 7.5.2.3 Economic water productivity benchmarks in Taewa The concept for WUE needs to focus on achieving more cash per unit of water used, apart from sustaining the environment and gaining more fruit yield per volume of water used, in order to sustain profitability in cases of high water cost and water scarcity (Aldaya et al., 2008). The economic water productivity in this study reports high EWP under partially irrigated treatments. The EWP ranged from 13.2 to 33.5 NZ$ m - 3 for cultivars and 20.7 to 23.2 NZ$ m - 3 for water regimes in 2010. In 2011, EWP ranged from 13.0 to 19.3 NZ$ m - 3 for cultivars and 14.6 to 17.0 NZ$ m - 3 for water regimes. The decline in average EWP for both cultivars and water regimes in 2010/ 2011 indicates the negative economic implication of potato psyllid infestation and weather on EWP. This finding on EWP sugges ts that WUE in potato is a product of different factors: optimal irrigation scheduling, pest and disease and cultivars and market price . Agria and Moonlight have high physical WUE, but they are not as economically productive under the same volume of water as Moe Moe. Similarly, the irrigation scheduling technology, for improving water use in Agria, is different for Tutaekuri. The results on EWP confirm the findings of Nielsen et al. (2005) that WUE , based on a dollar return per unit of water used, is sometimes high in those crops found with low evaporative demand (chickpea and canola) , rather than those crops with a high evaporative demand (cereals) (Nielsen et al., 20 05; Nielsen et al., 2006 ) . Likewise , market values or high values have determinature effect on EWP . Aldaya et al. (20 08) reported that the use of water for low value crops is sometimes the main problem, rather than water scarcity. Vegetables with high value were more economically productive, per volume of water (15 Euro/m 3 ? 27 NZ$/m 3 ), than grain cereal with less value (0.3 Euro/m 3 in Spain ( Aldaya et al., 2008) . In this study, heritage cultivars (Moe Moe, Kamo Kamo) demonstrated higher cash per volume of water used than modern cultivars with their high yield per unit of water. These results, together with those reported from CHAPTER 7 General Discussion and Conclusion 225 other authors; suggest that the market value of a product s hould be one of the driving forces in the allocation of water, in New Zealand. 7.5.3 Nitrogen use efficiency benchmarks in Taewa Nitrogen use efficiency is found to be highest under unlimited irrigation and limited N, but the consequence is that WUE is reduced (Chapter s 3 and 5). On the other hand, NUE wa s found to greatly differ between modern potato and Taewa. Zebarth et al. (2008) found that commercial potato cultivars have a higher or equal NUE , compared to Andean primitive cultivars; this finding is similar to this study. However, this study does not agree with Zerbarth?s earlier study (Zebarth et al., 2004) , which indicated that late maturity increases NUE : Taewa, although late maturing, has a low NUE compared to the short duration cultivar, Agria ( Zebarth et al., 2004) . In another similar study, Errebhi et al. (1999) assessed NUE in tuber bearing solanum species (wild s pecies and their hybrids) and commercial cultivars , at low and high N . I t was found that NUE was highest in wild species , with a minimal difference from Russet Burbank, but it was greater than that found in other modern potato cultivars (Errebhi et al., 1999) . Taewa, especially Tutaekuri , has low NUE and WUE , due to their self- selection for survival to adverse competition and environmental factors, whilst modern or commercial potato cultivars are either bred for high NUE or WUE ( Zebarth et al., 2008) . However, the comparison of Taewa NUE with wild species ( Errebhi et al., 1999) suggest that NUE also var ies between unimproved potato species (heritage or wild specises) with others exhibiting high NUE whilst others low NUE. An increase of application N from 80 to 240 kgN ha - 1 , has a marginal average yield increase of 23.8Kg kgN - 1 in modern potato, Agria whilst Taewa has a marginal average yield decrease of 9 kg kgN - 1 in Moe Moe and a marginal yield decrease of 53.4 kg kgN - 1 in Tutaekuri (Appendix 7.6 abcd) . This suggests that there are no marginal benefits in the Taewa yield with N being above 80 kg N ha - 1 , since Taewa is not bred for high N (Appendix 7.6 ). Taewa may be appropriate over modern potatoes when N resources are limited. Appendix 7.7 presents marginal productivity stratified by N and water regime , in order to measure marginal change in NUE , as one water regime is replaced by another. Marginal productivity is a satisfactory guide for farmers to make a balanced decision on how much N they should use with a particular water regime (Cooke, 1986 ) . In regards to this study, it is not rational for Taewa growers to operate above 80 kg N ha - 1 with all CHAPTER 7 General Discussion and Conclusion 226 water regimes, but modern potato can be produced at above 80 kg N ha - 1 with FI and PI ( Appendix 7.6 ). Maori people may select Taewa, due to its low N requirement, which easily meet their input investments, within their limited resources. 7.6 Comparison of Tutaekuri and Moe Moe Characteristics Tutaekuri is Solanum tuberosum subsp. andigena, whilst Moe Moe is Solanum tuberosum subsp. tuberosum (Harris, 2001). Throughout this study, T utaekuri exhibited fewer and larger stems with more branches, in addition to many small tubers and a higher shoot: root ratio , compared to Moe Moe. However, Chapters 4 and 5 indicate that Moe Moe and Tutaekuri have similar height and number of stems. O ccasionally, Moe Moe exhibited more tubers than Tutaekuri. On the other hand, the tuber yield, HI, WUE and NUE for Tutaekuri was lower than that for Moe Moe. Moe Moe managed to achieve high tuber yield and HI by modifying its tuber numbers with irrigation, which is different to Tutaekuri. Tutaekuri allocated more to stolons and roots . Harris ( 2001) also observed that Tutaekuri has long stolons. Tutaekuri responded to partial irrigation whilst Moe Moe performed well under full irrigation. Both Tutaekuri and Moe Moe required very low N. Despite some similarities, it can be concluded that specie?s variations are high within Taewa except that both cultivars were not bred specifically for high water and N use and both can provide a profitable business for Maori people , with the highest expectation for Moe Moe . 7.7 Economics of irrigation on Taewa Economic assessment of Taewa in relation to irrigation investments using the Net Present V alue method (NPV) is presented in Appendix 7.8. The economic results indicated that Moe Moe, had the highest additional gross revenue on investment income; additional annual revenue per ha from irrigation in the 1 st year; net present value ( Appendix 7.8.3; Appendix 7.8.4) and shortest repayment period, due to its high value and intermediate marginal yield increase with full irrigation and low N. M odern potato, Agria, was the least economic crop enterprise in relation to gross revenue on investment income; present value or additional annual revenue per ha from irrigation in the 1 st year; net present value and longer repayment period, due to its low market value compared to Taewa. CHAPTER 7 General Discussion and Conclusion 227 Tutaekur i had an intermediate gross revenue on investment income; present value or additional annual revenue per ha from irrigation in 1 st year; net present value; and intermediate repayment period, despite a low marginal yield with irrigation, due to its premium prices, partial moisture requirement and low N use . Moreover, the gross revenue for Tutaekuri is expandable by 38% with canopy management. Th is result suggests that fully irrigated Moe Moe and parti ally irrigated Tutaekuri, with low N , would be profitable investments for Taewa growers; due to their high value and low N use. G rowers are not advised to produce Tutaekuri under full irrigation and high N , in addition to Agria under partial irrigation and low N, because these production systems have negative NPV after an initial investment of NZ$65 57/ha ( Appendix 7.8.3; 7.8.4). Taewa, a traditional crop, can be produced economically, whilst supporting water conservation and low N input to the environment i n New Zealand. 7.8 Practical implications of the study for Taewa growers This study may contribute to Primary Industry policy on sustainable economic growth and improved economic, social and cultural benefits from the environment (MAFF, 2011) . The study may also contribute to the resource efficiency policy of the Ministry of Environment in New Zealand on achieving environmental standards, whilst sustaining and improving social and economic development (Miskell, 2009) . The study may provide sustainability indicators for improving Taewa growers? prosperity in crop production and environmental management. It may also present part of New Zealand?s solution to economic water scarcity, which is expected to increase, by 2025 (IW M I, 2000, 2002). Small scale growers may also improve marginal returns, by reducing irrigation and N costs and improving yields through selection of genotypes with high WUE or toleran ce to water stress, suggested in this study. R esearch on heritage crops contributes to the Ne w Zealand Government?s policy on improving Maori land use and sustainable development (MAFF, 2011 ). Provision of innovative technology to Maori on natural resources management increases their authority, possession and protection outlined in Waitangi Treat y between Maori and the British Crown on 6 th February, 1840 (Latiner, 2011). This study achieves part of this policy by supporting the livelihoods of Taewa growers and society though cultural economy which is rarely considered (Miskell, 2009). It also deli vers scientific information to protect and improve resources of cultural value to Maori community CHAPTER 7 General Discussion and Conclusion 228 (MAFF, 2011). Irrigation and canopy management study on Taewa can be one of the novel strategies for increasing Taewa products in the ?new economic space? and ?cultural resilience? among Taewa growers (Lambert, 2008) . Taking on board the recommendations of this study is one way the New Zealand Government may ensure the biodiversity of New Zealand?s species and win- over Taewa growers to efficient resource use, t hrough heritage crops. 7.9 Conclusion and suggestions for future research The morphological and physiological characteristics of Taewa include higher vegetative growth; higher photosynthetic WUE ; lower leaf water potential; higher tuber dry matter content; and higher specific gravity than modern potatoes. M odern potatoes excelled in area of early tuberisation, tuber yield and HI . This study also shows that irrigation and N are paramount for enhancing photosynthetic WUE ; photosynthetic capacity ; and tuber yield ? regardless of canopy manipulation. N itrogen application is not always advantageous for Taewa. Canopy manipulation failed to enhance tuber yield, when high N wa s applied to Tutaekuri . It can be concluded that modern potatoes are more responsive to irrigation and N application than Taewa. Taewa use more water ( when available), due to late maturity , and are also tolerant to water stress in time of scarcity, unlike modern potatoes. As a result, irrigation and N are important for both Taew a and the modern potato cultivars ? although in different ways. M odern cultivars had higher WUE and NUE, than heritage cultivars. However, some heritage cultivars (Moe Moe and Kamokamo) have comparable yield and WUE capability to modern cultivars. The heritage cultivars? WUE is high when assessed in economic terms. The increased vegetative growth, the higher number of tubers and the disparity in appropriate agronomic practices (pest and disease control) contribute to the low yield and physical WUE commonly observed in heritage crops. Partial irrigation and low N combinations are recommended for Tutaekuri , whilst Moe Moe requires full irrigation , similar to modern potato, but with low N in contrast to modern potato. M anagement of the canopy increased the total yield and marketable tuber yield by 26% ( 20 - 33% ) and 38% ( 3 2 - 44% ) in Taewa cultivar, Tutaekuri . This resulted from the redistribution of dry matter from excessive vegeta tive growth to the tuber. Howeve r, the CHAPTER 7 General Discussion and Conclusion 229 final tuber yield depended on how canopy management prepared the plant to use water efficiently. Applying CCC at Day 25 and 30 DAE and canopy topping easily partitioned more assimilates to the roots, whilst applying CCC at Day 25 and 50 DAE delayed root development potentially mak ing the crop very sensitive to water stress. For this reason, application of CCC at Day 25 and 50 DAE would be suggested for irrigated conditions, whilst the remainder would suit both irrigated and rain- fed conditions. Taewa growers should apply mechanic and hormonal canopy manipulation, irrigation and pest and disease control strategies stipulated in this study in order to optimise water use and tuber productivity. The economic analysis of growing Taewa has also indicated that Taewa can be produced economically under small scale irrigation, with partial irrigation and low N input. Taewa is potentially a profitable business with proper water, N and canopy management as determined in this study. In this case, it can be concluded that most heritage crops have potential economic WUE based on premium market values whereas modern crops have potential physical WUE based on high yield. Hence, heritage crops can provide alternative land use to sustain water and N use whilst improving productivity and economic gains among small scale growers of New Zealand. It is apparent in this study that selection of Tutaekuri for improved HI is a good criterion for enhancing Taewa yield and WUE . 7.9.1 Future Research M ost detailed research on Taewa has been primarily social in nature, except the stud ies by Roskruge (199 9), Hayward (2002) and Harris (2001) . This thesis on Taewa and those aforementioned studies all highlight the need for further research in various agronomic areas, in order to promote and meet the demands for Taewa within various potential niche markets. Then if warranted, t here is a need to consider Taewa response to a wide range of water and N tre atments and to study how Taewa responds to N increase from zero , in order to determine optimal production levels. F ield or glasshouse investigations on why Taewa genotypes have better yields under low N than high N fertilisation, compared to modern potatoes would be interesting. A molecular study would help to identify genes for improving NUE in modern potato or to determine how Taewa NUE and WUE traits control growth and biomass production, in a different way from modern potato. CHAPTER 7 General Discussion and Conclusion 230 There is need to examine phenotyping for drought tolerance in Taewa genotypes, since they have exhibited a level of tolerance to water and N stress. However, this study did not observe the cultivars? degree of tolerance to chronic and transient drought, or heat tolerance. This study has also demonstrated that drought increases root dry matter in Taewa, but root length and diameter were not investigated. A thorough investigation is needed on root architecture imaging, and root expression mapping could help to identify desirable root traits for the development of cultivars with desirable root: shoot ratio and HI, which favour both tuber yield and biomass production from Taewa. These investigations would help breeders to determine surrogate traits that are related to low N soils or drought tolerance in Taewa. For organic farming purposes, research is required on how Taewa responds to farmyard manure, compost and biosolids, or integrated organic - inorganic fertiliser management, under varied water regimes. There is also a need to develop a crop simulation model specifically for Taewa, in order to help growers predict growth, development and productivity of Taewa, at different N and water environment s. A potato calculator (Jamieson et al. 2004) , which is used by a number of growers and researchers, does not fit many of Taewa?s physiological and morphological characteristics. 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REFER ENCES 250 251 APPENDICES APPENDICES 252 Appendix 3.1 Effect of water regime, nitrogen and cultivars on volumetric soil moisture content (%) in the glasshouse, 2009 APPENDICES 253 Appendix 3.2 Change of A n and gs in potatoes during the growing season in the glasshouse 2009; Error bars represent ?SEM (a) (b) APPENDICES 254 Appendix 3.3 Interaction between potato cultivar, irrigation and N on DMC%. Error bar represents ?SEM. Appendix 3. 4 Specific gravity and tuber dry matter content (%) relationship for four potato cultivars grown in glasshouse, 2009 APPENDICES 255 Appendix 4.4.1 Precipitation (Pe), irrigation (I), deep percolation (Dp), soil moisture change (?S), actual evapotranspiration (ET a) , and crop water use [ETc or CWU = Pe + I ?Dp + ?S ] per ha in mm from 10th Nov., 2009 to May, 2010 APPENDICES 256 Appendix 4.4.2 Effect of irrigation and cultivars on volumetric soil moisture content (%) in the field, 4 th January 2009 to 11 th May, 2010 APPENDICES 257 Appendix 4.4.3 Photosynthetic WUE (?molCO 2 /m molH 2 O) and Net Photosynthesis (?molCO 2 m 2 s- 1 ) for Taewa and modern potato cultivars under irrigation and rain- fed conditions at different days after emergence, 2010 APPENDICES 258 Appendix 4.4.4 Proportion of dry matter partitioning in four potato cultivars after 100 days from planting APPENDIX 259 Appendix 4.4.5 Relationship of number of tuber with mean tuber weight (a) and harvest index (b) APPENDIX 260 Appendix 4.4.6 Relationships between (a) specific gravity and tuber dry matter content; (b) specific gravity and total sugars in potato cultivars APPENDIX 261 Appendix 5.1 (a) Effect of water regime, nitrogen and cultivars on volumetric soil moisture content (%) after 76 days from planting, 2010/ 2011 APPENDIX 262 Appendix 5.1 (b) Cumulative potential evapotranspiration (mm) and crop water use (mm) in three water regimes in 2010/ 2011 APPENDIX 263 Appendix 5.2 Interaction between potato cultivars and water regime on plant height (a), stems per plant (b), number of branches per plant (c) and interaction between potato cultivars and N on stems per plant (d) APPENDIX 264 APPENDIX 265 Appendix 5.3 Interaction between water regime*cultivar (a) and cultivar * nitrogen (b) on Tomato/ Potato psyllid infestation. Error bar represents ?SEM. APPENDIX 266 Appendix 5.4 Potato tuber yield - water relationship (a - c) and yield response factor , k y (d - f) APPENDIX 267 APPENDIX 268 Appendix 6.1 Proportion of dry matter partition to leaves, stems, roots and tubers in Tutaekuri under different nitrogen and canopy manipulations Appendix 6.2 The relationship of gaseous exchange parameters in Tutaekuri APPENDIX 269 Appendix 7. 1 Daily evapotranspiration during the two growing seasons, October 2009 to June 2010 and October 2010 to April, 201 1 at Massey University, Palmerston North Campus, New Zealand. APPENDIX 270 Appendix 7. 2 Difference in Taewa tuber yields between two seasons (2009- 2010 and 2010- 2011) under same water regimes APPENDIX 271 Appendix 7.3 Spray schedule and type of pesticides used in 2010/ 2011 APPENDIX 272 Appendix 7. 4 Total water footprints of growing Taewa and modern potato cultivars under different irrigation regimes, 2010/ 2011. Error bar represent ?SEM. APPENDIX 273 Appendix 7. 5 Optimal WUE benchmarks in Taewa and modern potato based on 2009- 2010 and 2010- 2011 studies APPENDIX 274 Appendix 7. 6 (abcd) Marginal productivity of Taewa and modern potato as affected by amount of N and water regime APPENDIX 275 APPENDIX 276 Appendix 7. 7 The relationship between total tuber and specific gravity (SG) and tuber dry matter content ( DM %). APPENDIX 277 Appendix 7.8 The economic feasibility of Taewa in relation to irrigation investments The adoption of irrigation for Taewa cannot be relevant, if the achievement of increased yield and water conservation does not produce gains within the agricultural production and biological economies of New Zealand. Economic feasibility is essential, given that an irrigation system for Taewa would need extra investments i n irrigation equipment and operation for Taewa, compared to rain- fed production. Apart from determining strategies for improving Taewa production, this section assesses the impact of bringing irrigation into Taewa production: and its economic returns. An interpretation of Taewa yield into an applicable economic value, in comparison to modern potato cultivars, will help irrigation policy makers and Taewa growers to make informed investment decisions. The following section estimates fixed and annual operating costs and expected returns , based on a 5 ha small scale irrigation using a Trail Travel Irrigator and it discusses the economic implications of the system on Taewa production in New Zealand. 7.8.1 Method of investment analysis This investment analysis is based on a net profit value analysis (NPV), referr ed to as the total of present value of single project cash flow s of the same unit (FAO, 1997a ) . Net profit value was determined based on a Trail Travel irrigator system investment costing NZ$32,786.80 at 5 ha (NZ$6557.36/ha) (Table 7.8.1) and annual irrigation related operation costs ranging from NZ$1283.2 ? NZ$ 1580.70 (Table 7.8.2 ). The analysis focuses on extra marketable yield increase (thus the difference between partial or full irrigation and rain- fed marketable yield) in three potato cultivar enterprises . The production system is a combination of crop enterprises, with full irrigation or partial irrigation under low or high N levels , compared to a rain- fed system under low or high N levels (Table 7. 8.3). Each crop enterprise (Agria, Moe Moe, and Tutaekuri) had four batches of the production system to be assessed: two under full irrigation (low and high N) and two under partial irrigation (low and high N). At the beginning, the initial present value for all production systems w as determined as additional annual revenue. H owever, only the production system with the highest additional annual revenue per ha, from irrigation in the 1 st year of each crop enterprise, APPENDIX 278 was finally selected for NPV evaluation (Table 7.8.3). Subsequently, the last three NPVs presented are based on the best three selected production systems: one from each cultivar (Table 7. 8.3 ). Potato prices for New Zealand flu ctuate within seasons and over years. However, prices also vary within potato varieties, with Taewa fetching more than 2.5 times that of modern potato varieties, in local markets and super markets. Over the past five to eight years, the price for modern potato at the farm gate has ranged from NZ$ 200 - 300 per tonne, with a weighted average of NZ$285 per tonne , in 2004, to NZ$300 - 400 per tonne, with a weighted average of NZ$385 per tonne , based on the assumption that 85% of the crop held a high price and 15% held a low price (Table 7. 8.3). Unfortunately, Taewa has no marked price based per tonne at the farm gate and for the sake of this analysis a Taewa farm gate price of NZ$962 per tonne has been used, based on the assumption that its price at a local market is >2.5 times that of modern potato. The cost of irrigation in New Zealand is NZ$2 mm - 1 ha- 1 , according to Hedley et al. (2009a ). Table 7. 8.1 Small scale irrigation system: investment and a nnual fixed cost estimates in NZ$. Financial feasibility measures on variable irrigation costs are based on the methods used by AgriLINK NZ Ltd to calculate an economic analysis of potato production. All calculations were based on 1 ha , with the assumption of a 10 year investment at 10% interest rate. The NPV was calculated by subtracting the present value of cost from the present value of benefits, according to FAO ( 1997a ) , as presented in the equatio n below. APPENDIX 279 Where: NPV= net present value; C = net cash flows received at the end of year t; I= the initial investment outlay; r= the discount rate/interest rate; and t = the project?s duration in years (from zero to n). Table 7 .8.2 Annual ownership and operation costs for irrigation systems at full and partial irrigation scheduling 7.8.2 Economics of irrigation on Taewa Table 7. 8.3 indicates that irrigation increased the marketable tuber yield in all twelve combinations of the production system. Agria had the highest marginal marketable yield increase of 22.7 t ha - 1 under full irrigation and 240 kgN ha - 1 production systems (52 t ha- 1 less 29.3 t ha- 1 ) . The highest marketable yield increase for Moe Moe was 10.7 t ha - 1 under full irrigation and 80 kgN ha - 1 production systems (33 t ha- 1 less 22.3 t ha- 1 ) . The highest marketable yield increase for Tutaekuri was 9.4 t ha - 1 under partial irrigation and 80 kgN ha - 1 production systems (23 t ha- 1 less 13.6 t ha- 1 ) . However, among st the three enterprises aforementioned, Moe Moe, had the highest additional gross revenue on investment income (NZ$ 10,293) ; present value or additional annual revenue per ha from irrigation in the 1 st year (NZ$ 8713) ; net present value (NZ52, 25 3.40) ( Table 7.8.3; Table 7.8.4) ; and shortest repayment period (0.75 years), due to its high value and intermediate marginal yield increase with full irrigation and low N. Regardless of the highest yield increase with full irrigation and high N in modern potato, Agria, i t was the least economic crop enterprise in relation to gross revenue on investment income (NZ$ 8,740) ; present value or additional annual revenue per ha from irrigation in the 1 st year (NZ$7,159 ) ; net present value (NZ41, 764.5) (Table 7.8.3) ; and longer repayment period (0.92 years), due to its low market value compared to Taewa NPV = ? ???? (??+??)?? ?? ??=0 Equation 7.1 APPENDIX 280 ( Table 7.8.3). Tutaekuri had an intermediate gross revenue on investment income (NZ$ 9,043) ; present value or additional annual revenue per ha from irrigation in 1 st year (NZ$7,760) ; net present value (NZ45, 819.90) ( Table 7.8.3) ; and intermediate repayment period (0.85 years) , despite a low marginal yield with irrigation, due to its novel value, partial moisture requirement and low N use . Moreover, the gross revenue for Tutaekuri is expandable by 38% (32 - 44%) with canopy manipulation. However, the repayment period amongst the three productions is within one season for all the production systems. Taewa is more affordable for Maori people a nd more suitable for environmental sustainability. The NPV analysis indicates that fully irrigated Moe Moe and partially irrigated Tutaekuri production systems , with low N , would be profitable investments for Taewa growers; due to their high value and low N use ( Table 7. 8.3) . Therefore, g rowers are not advised to produce Tutaekuri under full irrigation and high N , in addition to Agria under partial irrigation and low N , because these production systems have negative NPV after an initial investment of NZ$65 57.36/ha (Table 7.8.3). Taewa, a traditional crop, can be produced economically, whilst supporting water conservation and low N input to the environment in New Zealand. APPENDIX 281 Table 7. 8.3 Investment feasibility a nalysis for Trail Travel irrigated Taewa and modern potato APPENDIX 282 7.8.4 Net present value and pay back for Taewa under Trail Travel irrigator APPENDIX 283 PUBLICATIONS 1 Fandika, I.R Kemp, P.D., Millner, J.P. and D. Horne (2010) Water and nitrogen use efficiency in modern and Maori potato cultivars, Agronomy New Zealand, 40(2010) . 2 Fandika, I.R Kemp, P.D., Millner, J.P. and D. Horne (2011). Yield and water use efficiency in ( Cucurbita maxima Duchesne) Buttercup squash and ( Cucurbita pepo Linn) heritage pumpkin cultivar. Australian Journal of Crop Sciences , 5(6 ): 742- 747 APPENDIX 284