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. SOIL SURVEY AND ELECTROMAGNETIC INDUCTION - A MARLBOROUGH VINEYARD CASE STUDY A thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Soil Science ,.~,·• ',-1,.•, 1■1 Massey University "-iii' Institute of Natural Resources Pal me rs ton North , New Zealand Florencia Alliaume 2004 .. Alliaume Florencia (2003). Soil Survey and Electromagnetic Induction - A Marlborough Vineyard Case Study. Unpublished. M.Appl.Sc Thesis, Massey University, New Zealand. Abstract Differences in soil texture, soil nutrient status, available moisture and soil drainage, among other soil properties, contribute to the variability in fruit quality and yield within a vineyard. Accurate mapping of this variability could lead to an improved soil and vine sampling and management process, hence to a more uniform grape quality. Generally, maps derived from traditional soil surveys do not adequately account for the spatial variability of soils, making interpretation and soil management difficult. A geographic information system, a real-time kinematic differential global-positioning system and an electro-magnetic sensor, together with field work, are used to assess a soil survey in a ninety eight hectare vineyard in the Marlborough Region, New Zealand. Apparent electroconductivity (ECa) surveys were made during both dry (March) and wetter (September) soil conditions. Percentage and depth of gravel, gley horizons, soil bulk density, total available water content, chemical properties and depth to water table were all either measured in the field or estimated. Extremes in soil texture are found to correspond to high or low ECa values. The deep and shallow ECa survey made in March depicts soils with a high and a low percentage of coarse gravels. The deep ECa survey made in March also depicts deep soils with particles finer than 2 mm deeper in the profile. The highest and lowest total available water content estimates were also associated with highest and lowest ECa values. The ECa survey made in September apparently responds to water tables within 120 cm below the surface. Furthermore, from the contour survey made with the differential global-positioning system, a series of hollows and ridges are detected. A tendency for lower fertility on the ridges is observed. Nevertheless, it is not possible to accurately define soil variability from the ECa surveys. Although the information generated by the electro-magnetic sensor is useful, both field observations and the topographic survey are the main influences defining and mapping the five soil-geomorphic units identified in this project. The implications of the results for soil management are discussed. Suggestions for improving future trials using the electro-magnetic sensor for soil variability assessment and potential future research are also given. Finally, a lack of correspondence between potassium concentrations in soils and plants is investigated . A high potassium concentration in the water used for irrigation is found to be the possible cause of such results. Keywords: precision viticulture, soil electroconductivity, electromagnetic induction, soil properties, soil survey, GIS. A mi hermano y hermana, mama y papa, abue/os y abuelas, y a toda mi Familia y amigos en Uruguay. ii Acknowledgments To begin with, I would like to thank my supervisors Mike Tuohy and Alan Palmer and for their invaluable advice. Their suggestions, criticism, understanding and support made a difference to this project. To these two friends and tutors, my most special thanks. I am indebted to Callum Eastwood for kindly putting me in contact with Nobile Vineyard managers, helping me in field work and for friendly discussions. Thanks are also extended to Mathew Irwin for his professional and patient advice on the use of the software package. Their help was really invaluable for the development of this project. Research funds , for which I would like to express my great appreciation, were provided by Nobilo Vintners Ltd. and New Zealand Centre for Precision Agriculture I was personally funded by NZODA through a full scholarship and without their support this masterate project would not have been possible. In the field work I was helped immensely by Tim Laverack and Diane Stewart from Nobilo Ltd. Diane was always there to make sure I had everything I needed, while Tim always accompanied me in the field work and dug more than twenty pits in gravelly soils!! . He kindly measured the water depth in the wells over a period of three months. On many occasions I was also fortunate to count on their ingenious ideas too, which made my work a lot easier and for all that, I am sincerely thankful. Thanks must be extended to Warren Woodgyer who helped carry out the electroconductivity survey in the field. An important part of the laboratory work was carried out at the Massey University Fertilizer & Lime Research Centre. There I have to thank Lance Currie who made the chemical analysis for the soil samples. I also want to thank Ian Furkert and Glenys Wallace who were very helpful with facilitating the use of the necessary equipment. Anne West helped me with the statistic analysis and interpretations. Thank you very much to all of you. Special thanks to John Dando; I am very grateful for his tremendous help on the soil texture analyses. He not only facilitated the use of the laboratory and equipment, but was also very generous with his advice and comments. I would also like to dedicate a special paragraph to Carolyn Hedley who discussed the results with me, sharing with me her knowledge and experience with interpreting the electroconductivity survey and even opening my eyes on some occasions. To her, my very special thanks. iii It was a pleasure to work for so many hours at the Precision Agriculture Centre at Massey. There I have to thank John Holland and all the people working there that were always in the best mood, and we shared so many good moments. Many thanks to all the Latin American, Spanish, Indonesian, yanquis Ueje), Swiss, German, Kiwi and English friends who opened their hearts and made the experience in New Zealand unique. We shared unforgettable moments which will always be part of my life. Thanks to the unconditional support I received from my parents, Maria del Carmen Molfino and Carlos Alliaume and my brother Javier and sister Ines. Finally, a very special mention to my grannies, Juan Horacio Molfino and Maria Amelia Margenat for the example they set and the support which they have always given me. I could not have done it without having them in my heart and my mind. iv Table of Contents Abstract ... ........ ........... .................... .... .................................. ... ..................... ............ .. .. i Acknowledgments ................................... .......... ..................... ... ......... ...... ................. iii List of Tables ....... ........ ..... ............... ......... .. ............. ........ ..................... ................ ..... vii List of Figures .. ............ ............................ ................................... .... ....... ............ ....... vii General lntroduction ...... .. ... ................................ ................................... ........ ........... .. 1 1.1 Viticulture in the Marlborough Region ... ..... ..... ..................................................... 1 1.2 Soils, viticulture and precision technologies ......................................................... 1 1.3 Research importance, aims and objectives of the project. ... ................................ 2 Literature review ........... .......... ....... ....... ......... ........... ......... ........................... .............. 4 2.1 Introduction ....................................................................... ................ .................. 4 2.2 Soil properties affecting vine performance ........................................ ................... 4 2.2.1 Physical properties ................................................................ ........................ 5 2.2.2 Chemical properties ........................................... .. ..................... .................... 7 2.3 Potassium ............ ............................. ................................... .. .... ........... .............. 8 2.3.1 Potassium in grapes ....................... .............................................................. 8 2.3.2 Potassium in the soils ........................................ ............................. .............. 9 2.4 Precision Agriculture ...... ...... .. ..... ................................ ...................................... 11 2.5 Precision Agriculture Technology ..................................... .................. ... .. .......... 13 2.5.1 Geographical Information Systems ..................... ........................................ 13 2.5.2 Global Positioning Systems (GPS) ........................ .............. ... .................... . 14 2.5.3 Remote Sensing ... .. ............................................ ........................................ 15 2.5.4 Continuous soil data sensors ..................... ........................................ .. ....... 16 2.5.5 Variable rate technology .. .............................................................. ............ 17 2.6 Evaluation of soils using remote sensing and GIS technology ......................... .. 17 2. 7 Electrical conductivity principles and measurement.. ......................................... 18 2.7.1 ECprinciples ........................................ ...................................... ................ 19 2.7.2 Methods of measuring ECa ................... ........ ... .... ....................................... 21 2.7.3 Accuracy of electromagnetic induction survey ....... .. .................................... 22 2.8 Research on ECa - soil property correlations ..................................................... 25 2.9 ECa mapping applications ........ .. ............................................ ................... .. . ... .. 26 2.10 Precision viticulture opportunities ............................................................... ..... 28 2.11 Conclusion ............... .. .............................. .. .. .... ............................................... 32 Description of the study site .................................... ...... ............ .............................. 34 3.1 Location of Rarangi vineyard .................................... ......................................... 34 3 .2 The climate and its implications for viticulture .................................................... 35 3.3 Geology and Landscape .................................................................................... 39 3.4 Hydrogeology .... .............................................................................. ... ............... 41 3.4 The soi l pattern and implications for growing vines ...... .. ................................... .43 3.5 Summary ........................................................................................................... 45 V Soil electro-conductivity and topographic assessment.. ............ .... .... .. ...... ........... 46 4.1 Introduction .............. ........... ..... .. .............................. ..................... .......... .......... 46 4.2 Materials ...... ............. ... ................... .. ......... ..................................... .... ............... 46 4.2.1 RTK DGPS receiver and field computer system ............ ..................... .. ...... .46 4.2.2 Electromagnetic sensor (EM38) and vehicle .. .... ................. ... .............. ...... .48 4.2.3 Geographic Information Systems (GIS) .... ........... .................... .......... ......... .48 4.2.4 Vesper 1.0 ......................................................... ........................... .. ........ .... 49 4.2.4 Aerial photograph ................................. .. ...... ............................................ ... 50 4.3 Methodology ......................................... ............................................................. 50 4.3.1 Topographic and Electromagnetic conductivity survey ...................... .......... 50 4.3.2 Topographic maps .... .. ... .... .. .... ............. .. ........................... ......................... 51 4.3.3 ECa maps .................................................................................................... 53 4.4 Results ............................................................... ............................................... 54 4.5 Discussion ...................................... ............. ... .................................................. 62 4.5 Summary ....................................... ................. .. .. ........ .. .. .. ........................ ....... .. 64 Soil characteristics and water table assessment ... ......................... ........... ....... ..... 66 5.1 Introduction .... ....................... ................. ....... ............ ............................ ........... . 66 5.2 Materials ................ ........... ............ .................................. .. ................. ................ 66 5.3 Methodology .. .. .. ........................................................................................... ..... 67 5.3.1 Soil maps and vine rows ........... .................................................................. 67 5.3.2 Soil wells ............... ............ ... ..... ... .... .... ................................. .. ................... . 68 5.3.3 Soil physical analysis ...................... ............................................................ 68 5.3.5 Soil chemical analysis .......................... ...................... ............ ............... ...... 70 5.3.6 Particle shape assessment ................................... ..................... ................. 71 5.4 Results .............. ................ ................................... ...... .. ............................... ...... 72 5.4.1 Soil profiles descriptions and classification .................................................. 72 5.4.2 Soil physical analyses .................. .. ............................................................. 77 5.4.3 Water table levels and soil drainage .................... ... ..... ............................... 84 5.4.4 Pebble shape ......... ..................................................................................... 88 5.4.5 Soil chemical analyses ................... .... ................ ......................................... 89 5.5 Discussion ............. ..................................... .. ...... ............................................... 92 5.5.1 Soil profiles descriptions and classification .................. ................................ 92 5.5.2 Soil physical analyses ................................. ........................... .. ............ ....... 92 5.4.3 Water table levels and soil drainage ........... ..... .. ........... .. ...... ..... ................. 93 5.5.4 Pebble shape ............ .. ... ............. .... .. ................ ...... .................................... 94 5.5.5 Soil chemical analyses ........... ...... ...... .. ... ....................................... ............. 95 5.5.6 Potassium in vines and soils .............. ... .. .. .... .. ....... ...... ........ .................. .. .. . 96 5.6 Summary ........ ... ........... .. ................................................. .................. .. .. .. .. ...... .. 97 Correspondence of soil properties to ECa values ...................................... .......... 100 6.1 Introduction .... ....... ....... ..................................... ... .... .. ... .. ............ ....... .. ... .... .... 100 6.2 Methodology ...... ... .. .................... ... .. .............. ................ ....................... ........... 100 6 .3 Results .. ........ .. .. .. ................. .. ... ............. .................................... ... .. ............ .... 101 vi 6.3.1 Soil-geomorphic units ... .. .. ...................... ..... .. ....... .................. .. ..... .......... 102 6.3.2 Presence of water table ........................................................................... 106 6.4 Discussion ........ ................. ............................... ....................... ... ..................... 107 6.4.1 Soil texture variation ........................ ........................ ................................. 107 6.4.2 Soil chemical properties ........................................... ........ ... .... .. ................ 109 6.4.3 Total Available Water Content... ...... ......................... .. .... ... .. ................. ..... 110 6.4.4 Water table .......................................................................................... .... 110 6.5 Implications of find ings for vineyard management .......................................... . 111 6.6 Opportunities to improve future trials ............ ..................... .. .. ..... ..................... 112 Conclusions .......... ...... ................................................................ ................... .... ..... 113 References ........................................................................ ............. ......................... 115 Appendices ......................... ............................ .......... ................ ..... ......................... 124 Table 2.1 Table 2.2 Table 2.3 Table 3.1 Table 3.2 List of Tables Potassium levels ratings of different types of potassium ................ ......... 10 Approximate effect of various operational and ambient parameters on ECa measurements obtained on claypan soils ....................... ...... ...... 24 Potential uses of ECa maps .................................. .................................. 26 Predicted estimates of flood flows for the Wairau at Tuamarina .... ....... .. . 36 Probabilities of monthly low rainfalls at Blenheim. Equal or lower rainfalls than values showed are expected with the correspondent probabil ity ............... ................... .. .. ... ...................... ... ... ...... ... ............. .... 36 Table 3.3 Latitude-Temperature Index (L T l) estimated for main New Zealand grape growing regions and localities .............................. ......................... 38 Table 3.4 Average numbers of days of ground and air frost at Blenheim. Bold numbers indicate possibility of damage to vines ....... ... .. ...... ........ .......... 38 Table 3.5 Probabilities of frost occurrence, date of first and last frost, and duration of frost-free season at Blenheim (194 7-1975) .................... ....... 38 Table 3.6 Water chemistry data from Wairau Confined Aquifer from a well in the studied vineyard ............................................................... ...... .. ....... . .43 Table 4.1 Average deep soil ECa data for the western and eastern part of the vineyard, surveyed on two consecutive days in March ("dry" conditions) ..................................................................... ......................... 60 Table 4.2 Average deep soil ECa data for the western and eastern part of the vineyard, surveyed on two consecutive days in September ("wet conditions") . ............................................................... .... ......................... 60 Table 5.1 Average percentage of fine earth and clay content of three replicates of A horizons as a percentage of fine earth fractions ............................ ... 77 vii Table 5.2 Table 5.3 Table 5.4 Table 5.5 Table 5.6 Table 5.7 Table 5.8 Table 5.9 Table 6.1 Table 6.2 Table 6.3 Figure 2.1 Figure 2.2 Figure 2.3 Bulk density of the < 20 mm fraction for topsoils ................. .................... 82 Gravimetric soi l moisture content of the horizons A and C1 measured in July 2003 .................................. .. ........................................ 83 Estimate of the total available water content (TAWC) to 1 m depth ......... 83 Free water levels below the surface measured in wells for different dates ....................................................... ....... ............... ...... ......... ........ ... 85 Chemical analyses on the fine earth fraction topsoil samples taken in May and July . ......................... ............ ..... ...... .............. .... .... .......... .. ....... 90 Chemical analysis of topsoil averaged for samples from ridges and hollows. Main differences are highlighted .. ..................................... ......... 90 Reserve potassium (meq/100g) for topsoil samples ...... ...... .. .................. 91 Recommended soil quick test soil levels (MAF units) for wine grapes in New Zealand ................................................ ....................................... 95 Geomorphic position and availability of physical , chemical and water table information for the six soil-geomorphic units ........ .... .. ................... 101 A summary of soil chemical analysis for each soil-geomorphic unit. ..... 103 Soil morphological properties summarized for each soi l-geomorphic unit .................... .............................. ...................... .............. .................. 103 List of Figures Main processes for a site-specific management system ......................... 11 Soil electrical conductivity and grain size ............................................ .... 20 Schematic showing the operation of the Geonics EM38 soil conductivity sensor in vertical dipole orientation over deep topsoil (left) and shallow topsoi l (right) ............................................................... 21 Figure 2.4 The Veris 3100 soil conductivity mapping system employs two arrays to investigate soil at two depths, 0-25 cm and 0-75 cm .......... .... .. 22 Figure 2.5 Relative response of EM38 sensor versus depth ..... .. .. ....... .................... 23 Figure 3.1 Location of Rarangi vineyard (pink polygon), Marshland and Figure 3.2 Figure 3.3 Figure 3.4 Figure 3.5 Tuamarina. Approximate scale: 1 :55,000 ..... ..... .. ............................... ..... 34 Monthly rainfall normal at Marshland Catchment Station .......... .............. 35 Monthly mean, lowest and maximum temperatures at Blenheim station .......... .............................. ... ...................... .... .. ... .. ...... ................... 37 Frequencies of surface winds at Blenheim ......... ................... ............. ..... 39 The height of Rarangi Shallow Aquifer above sea level at Golf Club well #1901. High, normal and low values were calculated from data since 1989 .............................. .. ... ........................................... .... ....... ..... 42 viii Figure 4.1 Rover radio, Antenna, AgGPS 170 Field Computer and AgGPS 214 receiver ............................................................................................... .... 4 7 Figure 4.2 Non-contact EM38 sensor used to measure soil electrical conductivity ........... ...................................... ............... ...... .... .............. .. .. .48 Figure 4.3 RTK-DGPS receiver and EM38 pulled behind an ATV ........................... . 49 Figure 4.4 RTK-DGPS base station installed at the Rarangi Vineyard .......... ........... 51 Figure 4.5 Hill shade map of the vineyard calculated for an azimuth of 315° and an altitude of 45° .................................................... .. ....... .. .... .................. 54 Figure 4.6 Map of 20cm contours, sequence of ridges & hollows, and well positions ............................... .. ........ ........ ...... .......................................... 55 Figure 4.7 Photograph of the vineyard taken from the highest point in the west, looking east and showing the micro-topography (arrows are pointing at hollows) ... ......................................... .. ........ .. ............. ...... ............ ....... 56 Figure 4.8 Kriged and classified deep electrical conductivity map for the Rarangi vineyard from the March 2003 survey .............. .. ............ ...... ...... 57 Figure 4.9 Kriged and classified shallow electrical conductivity map for the Rarangi vineyard from the March 2003 survey ................ ..... .. ........... ..... 58 Figure 4.10 Kriged and classified deep electrical conductivity map for the Rarangi vineyard from the September 2003 survey ................................ 59 Figure 4.11 Comparison of deep ECa data of the same area measured on two different days, a) survey on the 18/09/2003 and b) survey on the 19/09/2003 ......... ......................... ..... .. .................... ................................. 60 Figure 4.12 Comparison of the deep ECa surveys made on a) March and b) September 2003 on the Rarangi Vineyard, and the sample sites for physical analysis ... .......... ...... .. ... ....... ......................... ................... .......... 61 Figure 5.1 Soil unit boundaries as mapped by Vincent (1999) (in black) and sample sites for physical and chemical analysis taken in this project. ..... 67 Figure 5.2 Soil at Site A, a hollow on the north eastern side of the vineyard ............ 73 Figure 5.3 Soil at Site E, a hollow on the western side of the vineyard ......... ... ......... 73 Figure 5.4 Soil at Site F, a hollow on the southeastern end of the vineyard ............. 74 Figure 5.5 Soil at Site C, a ridge in the centre of the vineyard ................ .. .............. .. 7 4 Figure 5.6 Landscape (top) and profile (bottom) at Site B, the southern end of the eastern stony ridge ...... ... ........................................................... ...... . 75 Figure 5.7 Photographs showing landscape (top) and profile (bottom) at Site D (ridge) ............ ........................................................................................ . 76 Figure 5.8 Particle size distributions of A horizons. Sites A to F ...... ........................ 79 Figure 5.9 Particle size distributions of C1 horizons. Sites A to F ........ .. ... ............... 80 Figure 5.10 Particle size distributions of lowest horizons. Sites A to F ....................... 81 Figure 5.11 Depth of horizons with more than 60% fine earth .................................... 82 Figure 5.12 Total Available Water Contents to 1 (red dots) and 1.2 m (black dots) depths estimated for samples in this project and by Vincent (1999) respectively ................................................................................. 84 ix Figure 5.13 Rainfall registered at Rarangi vineyard from middle September to middle November and water level fluctuation in wells 15, 2, and 20 ...... .. 86 Figure 5.14 Water tables <75 cm from surface in the Rarangi vineyard for different dates, during 2003, overlaying the hill shade map. Water depths in wells are illustrated in red circles. Areas affected were estimated from contours . ....... ........................... .......... ....... ......... .. ..... ..... 87 Figure 5.15 Map showing drainage classes. Data used for the classification included observations made in this project as well as the map generated by Vincent (1999) ............ ..... ............................... ................... 88 Figure 5.16. Classification of shapes of pebbles according to Zingg indices (Boggs, 2001 ) .. ..... .. ............... ............. ........ ................................ .......... .. 89 Figure 5.17 Map showing differently fertilised blocks of the Rarangi vineyard according to the schedule in 2003 ... ... .. .................... .. ...................... ..... 96 Figure 6.1 Aerial photograph of the Rarangi vineyard showing the sample sites for physical properties analysis and the soil-geomorphic units after an integration of the ECa maps with the soil and landscape data collected in the traditional way ........ .................... .. ................................ 102 Figure 6.2 Wells with water within 100 cm below the surface on 30th September, and soil conductivity map for 18th and 19th September . .. .. 106 Figure 6.3 Comparison of soil-geomorphic units obtained after integrating ECa data with soi l landscape data and soil units identified using the traditional soil survey method by Vincent (1999) ................... ... ......... ... . 108 X Chapter 1: General introduction CHAPTER 1 General Introduction 1.1 Viticulture in the Marlborough Region Viticulture and wine production in New Zealand have been increasing during the last twenty years. According to the Wine Institute of New Zealand (2003), the number of wineries increased from 131 to 398 between 1990 and 2003. In the same period, the producing vineyard area increased from 4,880 to 14,802 ha. The wine industry in New Zealand is decisively export orientated, with a growth from 8 million litres to 23 million litres exported in the last 10 years, representing NZ$ 246.4 millions FOB (free on board). Marlborough winegrowing area has grown rapidly and is now New Zealand 's largest and best-known one, with over 5,000 ha of established grapes (more than forty percent of the total New Zealand grape producing area), which produces half of the total New Zealand grape production. The worldwide interest in Marlborough wines, particularly Sauvignon Blanc and Chardonnay (and more recently Pinot Noir and Riesling), has resulted in a rate of development of about 1,200 ha per year of new vineyards (Wine Institute of New Zealand (2003). The region's environmental conditions have been crucial to such development. The typical free-draining, alluvial loams with gravelly sub-soils provide optimum growing conditions. High annual sunshine-hours (2450), cool climate during the hottest month (average 18°C), with cool nights and limited rainfall (642mm/year), allow a slow ripening process that contributes to the high quality of Marlborough wines. 1.2 Soils, viticulture and precision technologies Differences in soil properties, soil nutrient status and available moisture contribute to the variability in fruit quality, ripening and yield within a vineyard. An understanding of this variability and the relationships between manageable soil properties, grape yield and fruit quality could support more accurate soil and vine sampling and management. The development of new technologies has revolutionised the way in which soil information can be obtained more efficiently. Non-contact sensors based on electromagnetic induction technology have been shown to provide an effective basis 1 Chapter 1: General introduction for delineating interrelated physical, chemical and biological soil attributes (Johnson et al. , 2001a). One of these technologies is the Geonics electro-magnetic (EM38) sensor, which measures soil's apparent bulk electrical conductivity (EC8 ). With the data generated by the EM38, soil-sampling sites can be strategically selected and a targeted soil sample to calibrate the instrument can be taken (Bramley & Proffit, 2000). Once a relationship is established between ECa measures and one or more soil attributes, accurate maps showing the variability of different soil properties can be produced (Doerge, 2001 ). Adopting precision viticulture technologies like the EM38 and site-specific concepts, can lead to more accurate soil surveys and improved management opportunities (Lamb & Bramley, 2000). For example, the use of EM sensors, together with other precision viticulture tools, boosts the opportunity to harvest depending on quality specifications, to make a more effective use of inputs, reduce environmental risk, enhance sustainability and optimize the use of natural resources (Lamb & Bramley, 2000; Bramley & Proffit, 2000; Wolkowski , 2000). 1.3 Research importance, aims and objectives of the project A winery expansion scheme is being carried out at Rarangi in the Marlborough region, where 600 hectares are being planted. Soil properties are well known to influence vineyard performance, so an understanding of the soil's variability within the vineyard and the relationships that exist among the soil properties and the vines is required to adopt a site - specific vineyard management that could improve the grape production process. A lack of in-depth knowledge of the spatial variability of soil properties within the Rarangi vineyard planted mainly in 2001 , is limiting the successful adoption of site­ specific concepts and technology. Another unresolved question in the vineyard is the relatively high potassium concentrations found in plant samples. These values are higher than expected, being poorly correlated with the exchangeable potassium levels in the soils. EM38 measurements have the potential for mapping some soil properties differences, and some previous work has been done in New Zealand (Pitcher-Cambell, 2002; Hedley et al. , 2002). However, the proposed area to be studied is different to the majority of previous similar surveys. The large proportion of gravel and stones and slight soi l differences within the area of study constitute an extra challenge for both the interpretation of EM38 readings and the vineyard management. Hence, the growing wine industry in New Zealand will benefit from an increase in our knowledge and 2 Chapter 1: General introduction understanding of the relationship between soil properties and the electrical conductivity of the soils. A successful survey in this study would not only be helpful in assessing the likelihood of the vineyard response to targeted management, but would also promote the use of tools like the EM38, which promise a more accurate, quicker and cheaper method of mapping soil variability than the traditional manner. The main aim of this study is to use precision technologies (EM38, high-accuracy real­ time kinematic differential global-positioning system (RTK - DGPS)) and geographic information systems (GIS)) to produce accurate maps showing the distribution of main soil properties. A second aim of this project is to investigate possible reasons for the high potassium levels found in vines despite the low levels in soils. To achieve these aims, this project had the following objectives: 1) Carry out a detailed topographic and electromagnetic survey of the 98 ha of vineyard using the EM38 and RTK - DGPS, and map the variability found. 2) Identify and survey soil properties that are most important for the vines performance with a view to assessing the feasibil ity of crop response to targeted management. 3) Compare the ECa data with the detailed soils information collected in the traditional manner and interpret the electrical conductivity variability in terms of those characteristics identified in the previous above mentioned exercise. 4) Map the soil types and the variability of specific soil properties within the study area, implementing a geographic information system. 5) Determine the nutrient status of the soils. 6) Investigate the potassium (K) availability of the soils and possible causes for the high values found in plant samples compared with the low K values in the soils. 3