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. URINE NITROGEN IN HILL COUNTRY PASTURE SOILS A thesis presented in partial fulfilment of the requirements for a Doctor of Philosophy in Soil Science, Massey University W.M. SAMAN OEEPAL BOWATTE 2003 11 ABSTRACT In New Zealand the traditional way of building up nitrogen (N) fertility in pastures has been to apply phosphorus (P) fertilisers to provide adequate soil fertility for legume growth, which then provides N through biological N fixation. However, the marked responsiveness of hill pastures to N fertiliser indicates that this traditional approach may be placing a serious constraint on hill country production. At the same time, there is concern that the resulting elevated soil P levels may pose some environmental risk. Although the importance of soil N availability to hill country pasture production has long been recognised, there is surprisingly little infonnation available on N cycling in hill country pastures. This is because the limited research funding available has been directed mainly at detennining the requirements for P and suI fur (S) fertilisers, which have constituted the bulk of fertiliser expenditure in hill country. In order to develop best practice in the use of fertiliser N in hill country, infonnation is required on N flows in the soil-plant-animal system on the contrasting topographic land units that comprise hill pastures. The role of grazing animals and particularly the N transformations associated with urine patches are very important components of these N cycles. In this study, two field experiments were conducted at contrasting locations in North Island hill country pastures to investigate the fate of urine N. These field experiments were then followed by a laboratory incubation experiment that sought to clarify the effect of soil properties on subsequent transfonnations of urine N. The experimental results were then used, together with data from the literature, to model the N cycle for hill country pasture. In addition, to assess the N availability in hill pastures, an in situ N measurement technique using ion exchange resin membrane spikes was developed and evaluated. The first preliminary field experiment was carried out at the AgResearch Grassland hill country research site in Waipawa, North Island, New Zealand from 09 June 1 999 to 29 October 1 999. The major soil type was Waipawa Stony Silt Loam (PaIlic Soil). Three synthetic urine treatments (0, 200, 400 kg N/ha) were applied in a randomised complete block design and the experiment was repeated in a flat campsite and a steep site. At 1 III day after urine application (DAUA), the increase in the soil mineral N pool was close to or greater than the quantity of added urine N. The dominant form of mineral N throughout the experiment was NH4 + -N. This suggested that nitrification rates were low and that leaching losses ofN03--N would therefore be low. Only 1 8-27% of the urine N was recovered by the pasture. Estimates of the loss of urine N by ammonia volatiIisation were large, ranging from 2 1 -34% of added urine N. At the end of the experiment ( 1 42 DAUA), 34 -50% of added urine N appeared to have been immobilized into complex organic matter. The second field experiment was carried out at Ballantrae AgResearch hill country research station from 1 4 July 2000 to 1 2 December 2 000. The soil was N gamoko Silt Loam (Brown Soil). Three different rates (0, 280, 5 6 0 kg urine Nlha) of synthetic urine were applied as treatments and the experiment was repeated as a randomised complete block design on a flat campsite and a steep slope. Shortly after application, recovery of urine N as soil mineral N was greater than 1 00% ( 1 1 3 - 1 4 1 %) in the flat site. This increase in mineral N corresponded to a decrease in mineralisable N, suggesting organic matter mineralisation after urine application. During the first month after urine application, N&+-N was the dominant form of mineral N, but during the second month, N03--N was the dominant mineral N form. At the end of the experiment (88 DAUA), urine N recovery as mineral N was very low, ranging from 0-3 % . The rate of nitrification after urine application was higher in flat campsites than in steep slopes. Soil N03 --N levels in the 0- 1 0 cm soil depth in urine- treated plots at both sites decreased considerably between 30 and 45 DAUA. A simple model developed in Microsoft Excel suggested that substantial leaching of urine N (9- 3 3 % of added urine N) was likely to have taken place. Urine N recovery by herbage in this experiment was low ( 1 - 1 4% of added urine N ). Estimates of the loss of urine N through volatilisation were large, ranging from 24-5 1 % of added urine N . At the end of the experiment the amounts of urine N estimated to have been immobilised into the soil organic matter ranged from 8-57% of that added. A laboratory incubation experiment was conducted using four soils collected from the flat and steep sites of the field experiments at Waipawa and Ballantrae together with three other soils collected from lowland sites (Kairanga silt loam, Karapoti silt loam and Manawatu sandy loam (Fluvial Recent Soils)) that had received substantial quantities of IV excretal N over several years. Field moist soil, equivalent to a weight of 1 00 g of dry soil, was placed in each of 3 6 small plastic cups for each soil type. Urine was collected from four cows during m ilking two weeks before the experiment. Urine was applied to 1 8 cups of each soil at the rate of 6 mL of urinel l 00 g dry soil (40 mg urine Ni l 00 g dry soil) . The remaining 1 8 cups were used as controls . No solution was added to the control cups. In contrast to the field experiments, there was little evidence of an initial priming effect, with mineral N levels 3 DAUA ranging from 64-8 1 % of added urine N. Nitrification rates were highly variable (0. 3 to 1 8 .3 Ilg N03--N/g soil/day) across the seven soils. All lowland soils had higher nitrification rates than hill soils, while those soils collected from campsites had higher nitrifi cation rates than soils collected from steep slopes . Although nitrification could account for most o f the disappearance o f soil NH4 + -N from 3-45 DAUA, it was evident that mineralisable N and soil microbial biomass N also increased after urine application. A simulation model of a hill country N cycle developed in Microsoft Excel confirmed the importance of urine N in hil l country pastures. The model indicated that N outputs in animal products, together with losses through ammonia volatilisation and leaching from urine patches were likely to exceed the N inputs to hill pastures by legume N fixation, non symbiotic fixation and atmospheric deposition. This may be the reason for the observed high N responsiveness in hill country pastures. Pasture utilisation and excretal distribution in the paddock were the most important factors influencing the overall N balance in the paddock. M ore work is required to obtain information on these parameters in hill country pastures. The in situ N measurement technique using ion exchange resin membrane spikes proved to be a useful approach to monitoring the continuous changes in soil mineral N in the field experiments as well as in the incubation experiment. Resin spikes were able to detect apparently real differences in the availability of soil N - even when the standard 2 M KCl extraction could detect no differences. The potential of resin spikes to detect spatial variability in soil N status was also demonstrated. v A simple model developed in Visual Basic in Microsoft Excel to simulate the N adsorption by resin spike in soils demonstrated that soil moisture, soil temperature, soil N concentration and the time the resin spike is in the soil are all major determinants of the amount of N adsorbed to resin in soil . Vi ACKNOWLEDGEMENT I would like to thank following people and organisations for their part in seeing this project through to completion. My supervisors, Professor Russ Tillman, Mr Andrew Carran and Dr Allan Gillingham for their supervision, valuable suggestions, constructive criticism, encouragement, support and friendship during my study. Dr Dave S cotter for interesting lessons of modelling. Associate Professor Nanthi Bolan for his warm welcome on my first day at Massey University and the great help in finding accommodation and settling us in. James Hanly, Bob Toes and Phillip Theobald for their enormous support for laboratory and fieldwork, proof reading the thesis and especially the friendship throughout the study. Associate professor Mike Headly, Lance Currie, Ann West, ran Furkett, Mike Bretherton , Ross Wallace, Glenys Wallace, Dr. Loga Loganathan, Hera Kennedy and Denise BrunskiIl for their continuous support . Massey University for granting a Massey University Doctoral Scholarship and Helen E. Akers Ph.D. S cholarship . Managers and technical staff at Ballantrae AgResearch research station and the Waipawa AgResearch research stations for allowing me to conduct field experiments and supplying necessary resources. All past and present post graduate students; Sena, Tin, Asoka, Lui, Aravin, Tony, Steven, Khan, Fabio, Jamie, Rita, Thabo and many others for providing friendly atmosphere at Massey. Mrs. Connie Cathcart and her family for introducing this beautiful country to us and the warm-hearted assistance and friendship for settling to kiwi life . I especially thank to my loving wife Deepa and two lovely daughters D inithi and Tharushi for patient, understanding, support, belief and love through times when I needed it most. Finally I would like to dedicate this thesis to my mother and father and all my teachers for their effort to bring me up to this level. Vll TABLE OF CONTENTS ABSTRACT ........................................................................................................ 11 ACKNOWLEDGEMENT .................................................................................... VI TABLE OF CONTENTS ................................................................................... VII LIST OF TABLES ........................................................................................... Xlll LIST OF FIGURES ......................................................................................... XVI LIST OF PLATES ......................................................................................... XXIV CHAPTER ! INTRODUCTION INTRODUCTION ...................................................... ........................ .................. 1 2.1 2.2 2 .2 . 1 2 . 2 .2 2 .2 . 3 2 . 2 . 4 2.3 2 . 3 . 1 2 . 3 . 2 2 . 3 . 3 2 . 3 .4 2 . 3 . 5 2 . 3 . 6 2 . 3 . 7 2 . 3 . 8 2.4 CHAPTER 2 LITERATURE REVIEW Introduction ......................................................................................................... 4 New Zealand hill country ................................................................................... 4 Topography .. . . . . . .. . . ......... .... . . . . . . .... ..... . .. . . ...... . . . . . . . . ..... ..... . . . '" . . . . . . . . . . . . . . . . . . . . . . . . . 5 Soil .......... . . . . . .. ................................. .. .... . . . . .. .. . . . . .... . . . . ..... .. ....... . ..... . .. . ....... .. ... 5 Pasture composition ... . .... . . ...... . ........ ........ . .... . .. ...... . . . ... . ........ . ....... . ..... . ... .. .... 6 Nitrogen use in hill country .. ... . .... . . . .... . ......... . .... . ..... .. . ............. . . . ..... . . . ....... . . . 7 Nitrogen balances in different topographic units of hill country .................... 8 Pasture N uptake ..... . ........ .. . .... . . ............... . . . .... . . ..... . . . . . . . . . . . . ............ . . . . . . ...... . . 1 1 N fixation .. . . ...... . . . .... . . . . ...... ...... . .. ....... ............... . . . ...... . ....... . ........ . . . .... ... . ...... 1 1 Non-symbiotic N fixation and atmospheric deposition . ..... .. .. . . ...... . .. . ....... . . 1 3 Pasture utilisation . . ....... .. . .... . ... . ............ . ... . ............ . . . ... . . ................. . ... . . . . . . . .. 1 3 N remaining in pasture litter. . . . ..... . ............ . ... . ........ . ..... . . . .. . ...... .... . .... ..... . . . . . 1 4 N in animal products . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 Dung and urine N . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 Above ground N balance in hill country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6 Summary of literature review .......................................................................... 18 Vlll CHAPTER 3 FIELD INVESTIGATION OF THE FATE OF URINE NITROGEN ON A SUMMER DRY HILL COUNTRY PASTURE 3.1 Introduction ....................................................................................................... 20 3.2 Literature review ............................................................................................... 2 1 3 .2 . 1 3 . 2.2 3 . 2 . 3 3 . 2 . 3 . 1 3. 2 . 3 .2 3 . 2 . 3 . 3 3 . 2 . 3 .4 3 . 2 . 3 . 5 3 . 2 . 3 . 6 3 . 2 . 3 . 7 3 . 2 . 3 . 8 Nitrogen cycling through animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 Urine N . . . ......... . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 N transformations in the urine patch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Urea hydrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 Mineralisation and immobilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 Plant uptake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 0 Fixation t o clay minerals . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1 3.3 Materials and methods ...................................................................................... 41 3 . 3 . 1 3 . 3 .2 3 . 3 . 3 3 . 3 .4 3 . 3 . 5 3 . 3 . 6 3.4 3 . 4 . 1 3 . 4.2 3 .4 . 3 3 . 4. 4 3 .4 . 5 3 .4 . 6 3 .4 . 7 3 .4 . 8 3.5 3 . 5 . 1 3 . 5 . 2 3 . 5 . 3 3 . 5 . 4 3 . 5 . 5 3 . 5 . 6 Field site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1 Field trial design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Soil and plant sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Statistical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Results ................................................................................................................ 46 Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Statistical data interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 7 Mineral nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Ammonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1 Mineralisable N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . 5 2 Pasture response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8 Discussion ........................................................................................................... 59 Urine N recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9 Mineral N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Nitrification and leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Pasture response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Mineralisation and immobilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 IX 3 . 5 . 7 Comparison o f urine N transformations at two sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.6 Conclusions ........................................................................................................ 68 CHAPTER 4 DEVELOPMENT OF ION EXCHANGE RESIN MEMBRANE SPIKES FOR CONTINUOUS MONITORING OF AVAILABLE SOIL NITROGEN IN HILL COUNTRY PASTURE 4.1 Introduction ..................... .......... . . . ............... ............................. . . . ...................... 70 4.2 Literature review .............................................. .... ...................................... ....... 7 1 4 . 2 . 1 4 . 2 . 2 4 . 2 . 3 Ion exchange resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1 Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Ion exchange resin use in recent soil research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.3 Development of the ion exchange resin membrane spike ..... ......................... 77 4. 3 . 1 4 . 3 .2 4 . 3 . 3 4 . 3 .4 4 . 3 . 5 Experiment 1 : Preliminary assessment o f the ability of resin strips to adsorb mineral N from Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Experiment 2 : Assessment of variability with resin spikes . . . . . . . . . . . . . . . . . . . . . . . . . 78 Experiment 3: Optimization o f resin spike construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Experiment 4 : Optimization o f resin spike construction II . . . . . . . . . . . . . . . . . . . . . . . . . 80 Experiment 5: Evaluation of resin spike variability in soil . . . . . . . . . . . . . . . . . . . . . . . . . 8 1 4.4 N adsorption to resin membranes .............. ...... .............. ............ .............. ........ 82 4 . 4 . 1 4.4. 1 . 1 4.4. 1 .2 N adsorption to resin spikes over time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Experiment 1 : N adsorption from solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Experiment 2: N adsorption from soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8 4.5 Resin spikes performance in field ............................................. . . ..................... 9 1 4 . 5 . 1 4 . 5 .2 Field experiment 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1 Field experiment 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 4.6 Modelling of in situ N adsorption to resin membrane spikes ........................ 96 4 . 6 . 1 4 . 6 . 2 4 . 6 . 3 4 . 6 . 4 4 . 6.4. 1 4 . 6 .4.2 4 . 6 .4 . 3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 Basic equations for solute diffusion i n soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Model development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 00 Model output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 5 The effect of time o f burial o n N adsorption b y a resin spike i n soil . . . . 1 05 Effect of soil moisture on N adsorption by resin spikes . . . . . . . . . . . . . . . . . . . . . . . 1 09 E ffect of initial soil N concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1 x 4 . 6 .4.4 Effect of temperature on N adsorption by resin spike in soi! . . . . . . . . . . . . . . . . . . . . l l l 4.6 Recommended procedure ............................................................................... 1 12 4.8 Discussion ......................................................................................................... 1 1 4 CHAPTER S FIELD INVESTIGATION OF NITROGEN DYNAMICS UNDER URINE PATCHES IN NORTH ISLAND HILL COUNTRY PASTURE 5.1 Introduction ..................................................................................................... 1 1 8 5.2 Materials and methods ..... ............................................... ................... ............. 1 19 5 .2 . 1 5 . 2 .2 5 .2 . 3 5 . 2 .4 5 . 2 . 5 5 . 2 .6 5 . 2 . 7 5 .2 . 8 5 .2 . 9 5 .2 . 1 0 Site description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 9 Field layout and soil sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 9 Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 20 Soil sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 1 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 1 Soil mineral and mineralisable nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 1 Dissolved organic carbon and dissolved organic nitrogen . . .... .. . . . .. . . . . . . . . . . . 1 22 Resin-adsorbed nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 22 Plant dry matter production and pasture nitrogen uptake . . . . . . . . . . . . . . . . . . . . . . . . . 1 22 Statistical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 23 5.3 Results .............................................................................................................. 1 23 5 . 3 . 1 5 . 3 .2 5 . 3 . 3 5 . 3 .4 5 . 3 . 5 5 . 3 . 6 5 . 3 . 6. 1 5 . 3 . 7 5 . 3 . 8 5 . 3 . 9 5 . 3 . 1 0 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 23 Statistical interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 25 Mineral nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 5 Ammonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 8 Nitrate . . . . . . . . . . . . . . . . .. . . . . . . . .. . ..... . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 1 Perfonnance of resin spikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 3 Relationships between 2 M KCI -extractable N and resin-adsorbed . 1 3 5 Mineralisable N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 7 Pasture response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 1 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 44 Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. .. . ... .. . ... . . . . . . ... .. .. . . . . . . . . . .. . . . . . . . . . . . . . . . . 1 46 5 . 3 . 1 0 . 1 5 . 3 . 1 0. 2 Leaching model development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 46 Leaching model output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 5 0 5 . 3 . 1 1 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 1 54 5.4 Discussion ......................................................................................................... 158 5 .4 . 1 5 .4.2 5 .4 . 3 5 . 4.4 5 .4 . 5 5 .4 . 6 5 .4.7 5 . 4 . 8 5 .4 . 9 Xl Urine N recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 8 Mineral N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6 1 Priming effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 1 62 Ammonia volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 64 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 65 Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 65 Pasture response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 67 Denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 68 Immobilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 68 5.5 Conclusions ...................................................................................................... 1 69 CHAPTER 6 LABORATARY INCUBATION STUDY OF NITROGEN TRANSFORMATIONS IN HILL COUNTRY AND LOWLAND PASTURE SOILS AFTER APPLICATION OF URINE 6.1 Introduction ..................................................................................................... 1 70 6.2 Materials and methods .................................................................................... 171 6. 2 . 1 6.2.2 6 . 2 . 3 6 . 2 . 3 . 1 6 . 2 . 3 . 2 6 . 2 . 3 . 3 6 . 2 . 3 .4 6 .2 . 3 . 5 6 . 2 . 3 . 6 6 . 2 . 3 . 7 6 . 2 . 3 . 8 6.2.4 Soils used for the incubation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 1 Experimental procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 1 Chemical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 73 Mineral nitrogen (NH/-N and N03--N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 73 Total dissolved nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 73 Dissolved organic carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 73 Microbial carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . 1 74 Microbial nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 74 Total carbon and total nitrogen in soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 74 Hot water soluble carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 74 Clay fixed nitrogen . . . . . . . . . . .. . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 74 Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 75 6.3 Results .............................................................................................................. 17 5 6.3 . 1 6 . 3 . 2 6 . 3 . 3 6 . 3 . 4 6.3 . 5 6 . 3 . 6 6 . 3 . 7 6.4 6.4 . 1 Organic matter quality of tested soils . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 5 Mineral N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 82 Ammonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 84 Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 87 Mineralisable N . . . . . . . . . . . . . . . .. . . . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 89 Dissolved organic carbon (DOC) . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 9 1 Soil microbial biomass (SMB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . __ . . . . . . . . . . . . . . . 1 9 1 Discussion ......................................................................................................... 194 Nitrification . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 1 98 6.4.2 Relationships between resin-adsorbed N and O.SM K2S04 - extractable N Xll ..... . . . . ...... . . . . . ........ . . . .. . . . . . .. .. .. . . . . . . . . . . . . . . . ..... . . . . . . .. . . . . . . . . . . . . .... . . . . . .. . .. . . . . . . . . . .. . . . . . . 204 6.5 Conclusion ................... ....................................... .................. ............................ 207 CHAPTER 7 MODELLING THE NITROGEN CYCLE IN SHEEP GRAZED NORTH ISLAND HILL COUNTRY PASTURE 7.1 Introduction ...................................................... ........................................ ....... 209 7.2 Model inputs and development ....................... ................... ........ .................... 209 7.3 Model outputs .......................................................................... .... .................... 214 7.4 Sensitivity of the model to different conditions ............................................ 220 7.4. 1 Impact of excretal distribution . . . . . . .. . . . . . . . . . . . . . . . . ..... . . . . ...... . . . . . . . . . . . . . . . . .. . .. . . . . . . 22 1 7.4.2 Impact of pasture utilisation . . .. . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... . . . . . . . . . . . . . . .. . . . . . . . . . 222 7 . 4 . 3 Impact o f soil fertility, as affected by P fertiliser addition . . ...... . . .. . . .. . . . . . . . . 226 7.5 Improvement of efficiency of hill country N cycle ... . .. . ..................... . .......... 229 CHAPTER 8 SUMMARY AND IMPLICATIONS FOR FUTURE RESEARCH . . . . . .. ..... . . . . . . . . . 232 REFERENCES . . . ... . . . . . . ... ... . . . . . . . ... . . . . ...... . . . . . . . . . . .... . . . . . ........ . .... . . . . . . . . . ... ... . ... . . .... 241 APPENDIX 1 .................................................................................................. 261 APPENDIX 2 .................................................................................................. 263 APPENDIX 3 .................................................................................................. 271 APPENDIX 4 .................................................................................................. 274 LIST OF TABLES CHAPTER 2 Table 2. 1 Calculation of amount of dung and urine N derived from on each Xlll s lope category in the notional 1 ha paddock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 Table 2.2 N balance on different land slopes within a notional sheep-grazed hill pasture. (Values are based on Fig. 2 . 1 and Fig. 2 . 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6 Table 2.3 N inputs and N surplus in the notional 1 ha hil l country paddock. Data on N inputs per ha and N surplus per ha are from Table 2.2 and proportions of land in each slope category are from Table 2 . 1 and Gillingham ( 1 97 8 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 CHAPTER 3 Table 3 . 1 The partition of urinary nitrogen (Doak, 1 952) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 Table 3 .2 Constituents of the synthetic urine solution (PH= 7 . 8 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 Table 3 .3 . Treatments used in the experiment. . . . . . . ... . . ... . . . . . . .. .. . . . .......... . .. .................. .43 Table 3 .4 Apparent recovery of urine N as mineral Nand mineralisable N after urine application (kg N/ha/7 .5 cm depth) in the soil profile (0- 1 5 cm) i .e . all values are treatment minus control . * = did not measure . .............. .49 Table 3 .5 Mineralisable N levels (kg Nlha) in control soil s at different depths. Values are the average of soils sampled 27, 1 00 and 1 42 DAUA. . . . . . . . . . . . . 53 Table 3 .6 Pasture DM production and N uptake as effected by urine application ..... 5 8 Table 3 . 7 Effect of urine treatments on ammonia volatilization ........................ . ....... 59 Table 3 . 8 Apparent fate of urine NH/-N from 1 -27 DAUA (A) and 2 7 - 1 00 DAUA (B). All quantities are expressed as kg Nlha . . ............................... 64 Table 3 .9 Soil fertility indices of the two sites ........... ......... '" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 CHAPTER 4 Table 4. 1 Resin-adsorbed N (flg-N/5 cm2/3 days) from two different pasture plots . ....................................................................................... ...... .............. 78 Table 4.2 Resin-adsorbed N (flg-N/5 cm2/day) from N&N03 solution containing 1 0 flg/mL NH/-N and 1 0 )..l.g/mL N03·-N . ........ ..................... 79 Table 4.3 Adsorption ofN (llg-N/5 cm2/day) by glued spikes and fresh resin membranes from 25 mL samples ofNH4N03 solution containing XIV 1 0 Ilg NH/- N/mL and 1 0 Ilg N03'-N/mL over a day . . . . . . . . . . . .. .... . . . ......... . . 79 Table 4.4 N adsorption (llg-N/5 cm2/day) to resin spikes immersed in NH4N03 solution containing 1 0 Ilg/mL NH/-N and 1 0 IlglmL N03'-N for a day . . 80 Table 4.5 N adsorption to resin spike from homogeneous soil (flg-N/5 cm2/7 days) . ..................................................... .................. . .. . .. . . ... 8 1 Table 4.6 Estimation of resin-ads or bed N03'-N from NH4N03 solution containing different initial quantities ofN03·-N . . . . .. . ..... . . . ........ . ............. ... 8 5 Table 4.7 Estimation of resin-ads or bed NH/-N from NH4N03 solutions containing different initial quantities ofNH/-N . . ....... .......... . . ... . .. . ... ........ 86 Table 4.8 Soil NH/-N and N03'-N assessed by 2 M KC} extraction and resin adsorption, together with pasture N uptake over 1 2 days at 2 sites. Means with common letters are not significantly different (P<0.05) within a column at each site . .. . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . .... . . . . . .. . .. . . . ... . . . .. ... . . ..... 92 Table 4.9 Levels of mineral N in two soils as measured by 2 M KCI extraction and resin spikes. Measurements were made over a 7 day period in the Table 5 . 1 field and also after incubation for 7 days in the laboratory . ................. . . ... 9 5 CHAPTER S Treatments used in the experiment at Ballantrae AgResearch hill country research station investigating the fate of simulated urine N applied to hill country pasture . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . .. . . . .. . . . . . . . ... . . . . . . . . . . . 1 20 Table 5 . 1A Constituents of the synthetic urine solution (PH=7 .8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 20 Table 5 .2 Average meteorological conditions for 1 970- 1 995 at Ballantrae AgResearch Hill country research station (wind speed data was only available for 1 994) . .... . . . ... . . . . .... . . . . . . . . . . . . . . . . .... . . .. . . . . . . . ... . ... . . . . . . . . . . . . . . . . . ... . . . . . . 1 24 Table 5.3 Net mineral N (extracted by 2 M KCI ) in the soil profile (0-30 cm) (i .e. treatment minus control values) . . ... . ....... . . . . . . . . . . . . . . . . . . . . ....... . . ... . . . ... . . . . . 1 27 Table 5.4 Mineralisable N levels (kglha) in control soils at different depths. Values are the average of soils from sampling times at 3, 1 2 and 27 DAUA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 8 Table 5 . 5 Pasture DM production, herbage N concentration and N uptake fol lowing urine application . . . . . . ... . . . .. . . . .... . . . . . . . . . . . . . . . . ... . . . . . . .. . . . . .... . .. .. .... . . ... 1 44 Table 5 .6 Quantities ofNH3 trapped by samplers and estimated losses ofNH3 by volatilisation . .......... ... . . . . . . . ............... ............. . . . . . . . . . . .. .... ....... . . ..... . . ....... 145 Table 5 . 7 Amounts of urine N lost through NH3 volatilisation and overall xv recovery of added urine N at 3 DAUA. # = data from Table 5 . 3 . . . . . . . . . . . . 1 45 Table 5 . 8 Example of leaching calculation by the model. Data extracted from leaching model of the F560 treatment. . . ....... . . . . . . ............. . . .. . . . . .. . . ... . . . .. . .... 1 49 Table 5 .9 Estimated leaching losses from urine treatments by the two models . .. ... 1 5 1 Table 5 . 1 0 Example of nitrification calculation. Calculations up to day 8 are presented for the F560 treatment plots . . . . ... ...... .. . .. . . ... . . .. . . . . . . . . . . . . . ...... . . . . . . . 1 5 5 CHAPTER 6 Table 6 . 1 Apparent fate of urine N at 3 DAUA. * (rate of urine N was 400 ) lg N/g soil) i .e . values are treatment minus control) .. . . .... . .. . . . .. . . . . . .......... ...... 1 94 Table 6.2 Quantitative comparison ofNH/-N decrease and N03--N increase in urine treated soils from 3-45 DAUA. (All values are in )lg N/g soil) . ..... 1 9 8 Table 6.3 Nitrification rates during first 15 DAUA in the experimental soils . ... . . . . . 1 99 CHAPTER 7 Table 7 . 1 Data used to evaluate the model. G= measured data of Gillingham ( 1 978), B= measured data of B lennerhassett (2002), T= Findings from this thesis . . . . . . . . . . . .. . . .. .. . . ..................... . . . . . . . .. . .. . . .. . .. ... . ......... . ......... ..... 2 1 4 Table 7.2 Modelled balances for individual slope categories and for the overall paddocks taking into account that campsites, easy slopes and steep slopes occupy 1 2 .2%, 45 .5% and 42 .3% of the paddock area respectively . . . . . ............ ............. ........ . .... .................. . .... .... . ......... . . ... . ........ 2 1 7 Table 7.3 Data used to evaluate the model on a paddock with a high level of P fertility. G = measured data of Gillingham ( 1 978), B = measured data Table 8. 1 of (Blennerhassett (2002), T = Findings from this thesis . . . . . . . . . . ...... . . . . . . . . 226 CHAPTER 8 Comparison between sustainable levels of pasture production with current N inputs and theoretical maximum pasture production in different slope categories of hill country ..... ....... .. .... . ... . . . . ... . . . . . . . . . ..... . . . . . . 23 9 Fig. 2 . 1 Fig. 2 .2 Fig. 3 . 1 Fig. 3 .2 Fig. 3 . 3 Fig. 3 .4 Fig. 3 . 5 Fig. 3 . 6 Fig. 3 . 7 Fig. 3 . 8 XVI LIST OF FIGURES CHAPTER 2 Above-ground N balances for hill country with a north facing aspect. All values are kg Nlha/yr . . . ... ................ . ....... . ................................ . . 9 Above-ground N balances for hill country with a south facing aspect. All values are kg N/ha/yr . .. ................................................. ........... 1 0 CHAPTER 3 Percentage urine N recovery in urine patches. Data extracted from Ball et al. , 1 979 (Palmerston North) and Carran et al., 1 982 (Gore) ................... ........................................ . . . ..................... . ... . . . . .............. 23 Four general patterns of nitrification observed by Steel et al. ( 1 980) when soils are perfused with .005M (NH4)zS04 ........... . ..... . . . . . . . ... 32 Relationships between INA (Initial Nitrification Activity) and total N (%) and C/N ratio of soil . The data are extracted from soils that showed the Type 1 and Type 2 nitrification patterns of Steel et al. ( 1 980) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Relationships between INA (Initial Nitrification Activity) and total N (%) and C/N ratio of soil . All the data presented in Steel et al. ( 1 980) were used for the relationships . ........... .. . ...... ....... ...... . . ....... . . 3 3 Daily rainfall during the experimental period . . . . . .. ......... .... ... . . ....... ... .... . . 46 Effect of urine application on soil (0- 1 5 cm) mineral N level. * = significant treatment differences were observed within a sampling at the same site. NS = no significant treatment differences were observed within a sampling at the same site ........... . ........ ............... . . ... . .... . 48 Effect of urine treatments on soil (0- 1 5 cm) NH/ -N. * = significant treatment differences were observed within the sampling time. NS = no significant treatment differences were observed within the sampling time . ...................................................... . . .............. ..................... 50 Effect of urine treatments on soil (0- 1 5 cm) N03 --N. * = significant treatment differences were observed within the sampling time. NS = no significant treatment differences were observed within the sampling time . . . ..... .......... . . . . . ..... . ........... ........ . . ... . .................. ...... . . ............ 5 2 Fig. 3 . 9 Fig. 3 . 1 0 Fig. 3 . 1 1 Fig. 3 . 1 2 Fig. 3 . 1 3 Fig. 3 . 1 4 Fig. 4. 1 Fig. 4.2 Fig. 4.3 Fig. 4.4 Fig. 4 .5 Fig. 4 .6 Fig. 4 .7 Effects of urine treatments on soil (0-7.5cm) mineralisable N levels at 27, 1 00, 142 DAUA. Treatments with common lower case letters do not differ (P<0.05) within a sampling day at the same site. Treatments at the same site with common upper case XVll letters do not differ at (P<0.05) between sampling days . . . . . . .. . . . . . . . . ... . . . . . . . . 53 Effect of urine treatments on pasture DM accumulation. Total DM accumulations at the same site with common upper case letters do not differ at the P<0.05 level . Treatments at the same site and at the same harvest with common lower case letters do not differ at the P<0.05 level. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Effect of urine treatments on pasture N accumulation. Total pasture N accumulations at the same site with common upper case letters do not differ at the P<0.05 level. Treatments at the same site and at the same harvest with common lower case letters do not differ at P<0.05 level. . . . . 57 Effect of urine treatments on ammonia volatilisation. Treatments with common letters within a site do not differ at the P<0.05 level . . . . . . . . . . 5 8 Total urine N recovery (%) during the experiment. . . . . . . . . . .. . .... . . . . . .. .. . . . .. . ... 60 Urine N recovery during the experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1 CHAPTER 4 Polymerization synthesis of a styrene sulfonic acid cation exchange resin (Harland, 1 994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Relationship between diffusion impedance factor and moisture content. (Logistic curve fit for the data in Fig. 4. 1 of Tinker and Nye (2000) .) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 N adsorption to resin spikes from different concentrations of NH4N03 solution. Each point represents the average of three replicates . . . . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . ...... . . . . . . . . .. . . .. . ..... . ... . . .. . . . . ... . . . . . ..... . .. . . . . . . . .. . . 83 Estimated and measured resin-adsorbed N03'-N from N�N03 solutions containing different initial quantities ofN03'- N . . . . . . . . . . . . . . . . . . . . . . . . 85 Estimated and measured resin-adsorbed NH/-N from NH4N03 solutions containing different initial concentrations ofNH/ -N. n = Selectivity coeffi(:ient of K+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 N adsorption by resin spikes with time from �N03 solution containing 1 0 �g NH/-N/mL and 1 0 �g N03'-N/mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 NH4 + -N levels during the incubation as measured by the 2 M KCI - extractable and Resin methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Fig. 4 .8 Fig. 4 .9 Fig. 4. 1 0 Fig. 4. 1 1 Fig. 4. 1 2 Fig. 4. 1 3 Fig. 4. 14 Fig. 4. 1 5 Fig. 4. 1 6 Fig. 4. 1 7 Fig. 4. 1 8 Fig. 4. 1 9 XVlll N 03--N levels during the incubation as measured by 2 M KCI -extractable and Resin methods . . . . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . 90 Notional box of soi l . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Modelled experimental soil cube with resin spike inserted, viewed from above. The anion exchange resin membrane is facing cells ( 1 0,9), ( 10, 1 0), ( 1 0, 1 1 ), and ( 1 0, 1 2) and the cation exchange resin facing the cells ( 1 1 ,9), ( 1 1 , 1 0), ( 1 1 , 1 1 ) and ( 1 1 , 1 2) . . . . . . . .... . ... . . . . . . . . . . . . . . . . . 1 00 Electrical conductivity of different NH4N03 concentrations at 20° C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 02 Measured and modelled N03'-N adsorption to resin spikes with time . . . . 1 06 Modelled N03'-N concentration (/ lg/cm3 soil solution) in each soil compartment (0.25 x 0.25 x 5 cm) 1 day after placement of the resin spike in soil . The asymmetrical depletion pattern is caused by the placement of the anion resin strip on the side of the spike apparently closest to the top of page. (This diagram shows only half of the system) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 07 Soil N03'-N (/lg/cell) distribution in each soil compartment (0.25x O.25x 1cm) 1 day after placement of the resin spike in soil . The resin spike is placed at 2-3 cm on the X axis and at 2.5 cm on the Y axis. The asymmetrical depletion pattern is caused by the placement of the anion resin strip on the side of the spike apparently closest to the reader. . . . . . . . . . ... .. . . . . . .. . . ............ ......... .... ......... . . . . . . . ... ..... ..... . . . 1 07 Modelled N03'-N concentration (/lg/cm3 soil solution) in each soil compartment (0.25 x 0.25 x 5 cm) 7 days after placement of the resin spike in soil (This diagram shows only half of the system). 1 08 Soil N03'-N (/lglcell) distribution in each soil compartment (0.25x 0.25x l cm) 7 days after placement of the resin spike in soi l . The resin spike is placed at 2-3 cm on the X axis and at 2 .5 cm on the Y axis . . . . . . . l 08 Modelled effect of soil moisture content on N03--N adsorption by resin spikes with time after burial. W = gravimetric moisture content. .. 1 09 Effect of soil moisture on soil N03--N (/ lglcell) distribution 7 days after placement of the resin spike in soil. The resin spike is placed at 2-3 cm on the X axis and at 2 .5 cm on the Y axis. The asymmetrical depletion pattern is caused by the placement of the resin strip on the side of the spike ' apparently closest' to the reader. . . . . . . . . . . . . .. . .. . . . . . . .... . . . . . . 1 1 0 Modelled effect of initial soil N03--N concentration (/ lg N03'-NI g soil) on N03--N adsorption by resin spikes with time after burial. The gravimetric moisture content is 0.26 (w/w) . . . . . . . . .. . . . . . .. . . . ... . . .... . . . ...... 1 1 1 Fig. 4.20 Fig. 4.2 1 Fig. 4.22 Fig. 5 . 1 Fig. 5 .2 Fig. 5 .3 Fig. 5 .4 Fig. 5 . 5 Fig. 5 .6 Fig. 5 .7 Fig. 5 . 8 Fig. 5 .9 Fig. 5 . 1 0 Fig. 5 . l 1 Fig. 5 . l 2 XlX Modelled effect of temperature on N adsorption by resin spikes with time. The moisture content of the soil is 0.26 (w/w) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2 Schematic diagram of resin spike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 3 Schematic diagram of processes controlling the available soil N . . . . . . . . . . . 1 1 5 CHAPTER 5 Rainfall during the experimental period ( 1 417/2000- 1 9/ 1 0/2000) . . . . . . . . . . 1 24 Air and soil temperature during the experimental period ( 1 4/7/2000- 1 9/ 1 0/2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 25 Effect of urine application on soil (0-30cm) mineral N levels . . . . . . . . . . . . . . . . 1 26 Effect of urine application on soil NH/ -N levels (O- I Q cm) as determined by 2 M KCl extraction and resin adsorption methods . . . . . . . . . 1 29 Quantities of 2 M KCI extractable NH/-N and N03--N in the 0-30 cm soil depth during the experimental period. Note. Change in scale between control and treated plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 30 Effect of urine application on soil N03--N levels (O- I Q cm) as determined by 2 M KCI -extraction and resin-absorption methods . . . . . . . . 1 32 Effect of urine treatments on resin-adsorbed N03--N at 5 5 to 97 DAUA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 34 Relationship between resin-adsorbed N and 2 M KCI extractable N when both steep and flat site data are used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 36 Relationships between (A) resin adsorbed N03--N and 2 M KCI ­ extractable N03--N. (B) Resin-adsorbed NH/-N and 2 M KCI adsorbed NH4+-N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 37 Effects of urine treatments on soil (0- 1 0 cm) mineralisable N levels at 3, 1 2, 27 days after urine application. Treatments with common upper case letters do not differ at P<0.05 level within a sampling day. Treatments with common lower case letters do not differ at P<0.05 level between sampling days of the same treatment. . . . . 1 3 9 Effect of urine application on soil mineralisable and mineral N levels (O- I Q cm depth) at 3, 1 2 and 27 days after urine application (DAUA) . . . 1 40 Relationship between increase in soil mineral N and decrease in soil mineralisable N from 3 to 1 2 and from 1 2 to 27 DAUA. . . . . . . . . . . . . . . . . . 1 4 1 Fig. 5 . 1 3 Fig. 5. 1 4 Fig. 5 . 1 5 Fig. 5 . 1 6 Fig. 5 . 1 7 Fig. 5 . 1 8 Fig. 5 . 1 9 Fig. 5 .20 Fig. 5 . 2 1 Fig. 5 .22 Fig. 5 .23 Fig. 5 .24 Effect of urine treatments on pasture DM accumulation at the flat and steep sites. Dry matter yields with common letters between treatments within same cut and same site do not differ at P<0 .05 . Total DM accumulation with common lowercase letters between xx treatments within same site do not di ffer at P<0 .05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 42 Effect of urine treatments on herbage N accumulation. Herbage N accumulations with common uppercase letters between treatments within the same cut and site do not differ at P<0 . 0 5 . Total herbage N accumulations with common lowercase letters between treatments within same site do not differ at P<0 . 0 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 43 Effect of urine treatments on ammonia volatilisation during the first 6 days after urine application. Values with common upper case letters between treatments within same site do not differ at P<0.05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 44 Estimated and measured 2 M KCI -extractable N03'-N in the 0- 1 0 cm soil depth during the experimental period. Arrows indicate measured 2 M KCI -extractable N03' N. Other marked data points ( .) are estimated 2 M KC I -extractable N03'-N values from the relationship with resin adsorbed N03'-N illustrated in Fig. 5 . 8 - . . . . . . . . . . . . . 1 49 Estimated quantities of soil N03'-N (g/m2) in the 1 0-20 cm and 20-30 cm depths from the two models during the experimental period . . 1 52 Estimated cumulative leaching of N03--N (g/m2) from 1 0-20 cm and 20-30 cm soil depths from urine treatments from the two models during the experimental period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 53 Schematic diagram to illustrate nitrification rate calculation . . . . . . . . . . . . . . . . . . 1 54 Cumulative daily nitrification during the experimental period . . . . . . . . . . . . . . . 1 5 6 Frequency distribution of daily nitrification rates calculated at each site for the period up to 45 DAUA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 8 Urine N recovery during the experimental period. The dotted line indicates the application rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 9 Urine N recoveries (%) during the experimental period, estimated as the sum of soil mineral N, NH3 volati lisation, plant uptake and leaching ofN03--N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 60 Resin adsorbed NH/-N (A) and N03--N (B) l evels during the experimental period in control treatments at both sites . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 62 Fig. 6. 1 Fig. 6.2 Fig. 6.3 Fig. 6.4 Fig. 6 .5 Fig. 6.6 Fig. 6.7 Fig. 6.8 Fig. 6.9 Fig. 6. 1 0 Fig. 6. 1 1 Fig. 6. 1 2 Fig. 6. 1 3 Fig. 6. 1 4 Fig. 6.1 5 Fig. 6. 1 6 XXI CHAPTER 6 S oil carbon related organic matter properties studied during the experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 77 Nitrogen related organic matter properties studied during the experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . 1 78 S oil carbon to nitrogen ratios in experimental soiL. . . . . . . . . ... . .. . . . . . . . . . . . . . . . . . . 1 79 Relationships between organic matter quality parameters . . . . . . . . . . . . . . . . . . . . . . 1 8 1 Effect of urine application on 0.5M K2S 04-extractable soil mineral N . (The statistical analysis of the data in this figure is included in Appendix 3) . ......................................................................... 1 83 Percentage of urine N recovered as soil mineral N at the beginning (3 DAUA) and end (45 DAUA) of the experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 84 E ffect of urine application on soil 0.5M K2S04-extractabl e NIL; + -N. (The statistical analysis of data i n this fi gure is included in Appendix 3) . ............................................................................................ 1 85 Effect of urine application on resin-adsorbed NIL; +-N. (The statistical analysis of data in this figure is included in Appendix 3) . ...... 1 86 Effect of urine application on 0.5 M K2 S04 -extractable soil N03--N. (The statistical analysis of data in this fi gure is included in Appendix 3) . ........................................................................................ .... 1 88 E ffect of urine application on resin-adsorbed N03--N over time. (The statistical analysis of data in this figure is included in Appendix 3 .) ...................... ...... ........... ......................... ............................ 1 89 Effect of urine application on soil mineralisable N with time. (The statistical analysis of data in this figure is included in Appendix 3) . ...... 1 90 E ffect of urine application on soil DOC levels. (The statistical analysis of data in this figure is included in the Appendix 3 ) . . . . . . . . . . . . . . ... 1 92 Effect of urine application on soil microbial biomass N with time. (The statistical analysis of data in this figure is included in Appendix 3) ............................................................................................. 1 93 The distribution ofNH/-N and N03'-N in urine treated soils with time after urine application . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 1 97 Comparison of nitrification of urine N and control soil N . . . . . . . . . . . . . . . . . . . . . . 200 Relationship between CIN ratio and nitrification rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 Fig. 6. 1 7 Fig. 6 . 1 8 Fig. 6 . 1 9 F ig. 6 .20 Fig. 7. 1 F ig. 7 . 2 F i g . 7.3 Fig. 7.4 Fig.7 .5 XXll Relationship between nitrification rate and the ratio of labile organic C to TC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Relationship between nitrification rate and soil pH of the experimental soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 Relationship between resin-adsorbed N and 0.5M K2S 04- extractable N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Relationships between resin-adsorbed N and 0 . 5M K2 S 04- extractable N in different soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 CHAPTER 7 Modelled N cycle in a hill country paddock with northerly aspect ( 1 2.2% campsite, 45.5% easy slope, 42.3% steep slope) . All values kg Nlha/yr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 5 Modelled N cycle in a hill country paddock with southerly aspect ( 1 2 .2% campsite, 45.5% easy slope, 42.3% steep slope) . All values are kg Nlha/yr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 6 Modelled N balance for two hill country paddocks with contrasting proportions of steep, easy and flat land. All values are kg Nlha/yr. F = N input by legume N fixation, non symbiotic fixation and atmospheric deposition, AT = Animal transfer, AP = Animal products, AV = Ammonia volatilisation, L = Leaching, P.u. = Pasture utilisation, Excretal N = Percentage of excretal N deposited on each slope category in that paddock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 N Balances for hill country paddocks with different excretal distributions. Values are kg Nlha/yr. Pasture DM production, proportion of clover in herbage and N concentration in herbage were as for the north aspect paddock in Table 7. 1 A. F = N input by legume N fixation, non symbiotic fixation and atmospheric deposition, AT= Animal transfer, AP = Animal products, AV = Ammonia volatilisation, L = Leaching, P.U. = Pasture utilisation, Excretal N = percentage of excretal N deposited on each slope category in that paddock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 N Balances for hill country paddocks with different pasture utilisations. Values are kg Nlha/yr. Pasture DM production, proportion of clover in herbage and N concentration in herbage were as for the north aspect paddock in Table 7. 1 A. F = N input by legume N fixation, non symbiotic fixation and atmospheric deposition, AT = Animal transfer, AP = Animal products, AV = Ammonia volatilisation, L = Leaching, P .u. = Pasture utilisation, Excretal N = percentage of excretal N deposited on each slope category in that paddock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Fig. 7.6 Fig. 7.7 N B alances for north aspect hill country paddocks under l o w P and high P conditions. Values are kg N/halyr. F = N input by l egume N fixation, non symbiotic fixation and atmospheric deposition, AT = Animal transfer, AP = Animal products, AV = Ammonia volatilisation, L = Leaching, P.D. = Pasture utilisation, Excretal N = percentage of excretal N deposited on each slope XXlll category in that paddock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 N Balances for south aspect hill country paddocks. Values are kg N/halyr. F = N input by legume N fixation, non s ymbiotic fixation and atmospheric deposition, AT = Animal transfer, AP = Animal products, AV = Ammonia volatilisation, L = Leaching, P.D. = Pasture utilisation, Excretal N = percentage of excretal N deposited on each slope category in that paddock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 XXlV LIST OF PLATES Plate 3 . 1 Ammonia volatilisation measurement using chamber methods (Ball et al. , 1 979; Theobald, 1 98 3 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Plate 3 .2 Ammonia volatilisation measurement using passive samplers (Carran et al., 2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27