Influence of different agricultural management systems on nitrogen leaching: results of lysimeter studies

The objective was to estimate the potential risk of N leaching into the groundwater under various types of agriculture by using lysimeter experiments on the nitrogen(N)‐cycle of various soil types. Results were obtained with 12 weighable, monolithic lysimeters with a surface area of 1 m², a total depth of 3 m, and free drainage. Mean annual N‐leaching losses of 5 to 44 kg ha^—1 and nitrate concentrations of the seepage water (leachate) between 80 and 200 mg l^—1 were measured during the period of intensive agricultural use. On fallow land with a well‐established grass vegetation, some nitrate was removed by the plants. As a result, the nitrate concentrations in the leachate were reduced significantly. Ecological farming measures generally reduced N leaching losses and kept the N‐concentration in the leachate below the German threshold value for drinking water with 50 mg l^—1 nitrate. However, ploughing in of clover or leguminous vegetation and the application of farmyard manure in autumn caused the nitrate concentration in the leachate to rise significantly above the mentioned threshold value.<?show $6#>     

Simulation of nitrogen dynamics in farmland areas of Denmark (1989–1993)

Abstract. Each year since 1986 information has been collected about the farming systems at intersections of a nationwide 7 km square grid in Denmark. These management data and corresponding soil analyses were used in the model DAISY to simulate water and nitrogen dynamics. The model was validated with respect to harvested dry matter yield and nitrogen content in the soil. Simulated nitrate leaching from farmland areas from 1 April 1989 to 31 March 1993 was related to precipitation zones, soil type, fertilizer strategies and cropping systems. The mean simulated nitrate leaching for the whole of Denmark was 74 kg N/ha/yr, with a large yearly variation in the period considered. The simulated nitrate leached from soils with a sandy subsoil corresponded to 51% of the applied fertilizer, twice that leached from soils with a loamy subsoil. The application of pig manure resulted in average leaching losses of 105 kg N/ha/yr. The simulated nitrate leaching losses at sites where only artificial fertilizer was applied were in the following order: cereal with undersown grass < crop followed by winter cereal or winter rape < cereal or rape without a catch crop < root crops without a catch crop. Where only artificial fertilizers were applied, the simulated mean annual leaching was 59 kg N/ha from spring barley and 40 kg N/ha from winter wheat. A map of simulated nitrate leaching in Denmark was produced using a Geographical Information System.     

The effect of crop, N-level, soil type and drainage on nitrate leaching from Danish soil

Abstract. Nitrate leaching measurements in Denmark were analysed to examine the effects of husbandry factors. The data comprised weekly measurements of drainage and nitrate concentration from pipe drains in six fields from 1971 to 1991, and weekly measurements of nitrate concentration in soil water, extracted by suction cups at a depth of 1 m, from 16 fields in 1988 to 1993. The soils varied from coarse sand to sandy clay loam.
The model used for analysing the data was: Y = exp (1.136–0.0628 clay + 0.00565N + crop ) D^0.416, with R²= 0.54, where Y is the nitrate leaching (kg N/ha per y), clay is the % clay in 0-25 cm depth (%), N is the average N-application in the rotation (kg/ha/y) and D is drainage (mm/y). The most important factor influencing leaching was the crop type. Grass and barley undersown with grass showed low rates of leaching (17-24 kg/ha/y). Winter cereal following a grass crop, beets, winter cereals following cereals and an autumn sown catch crop following cereals showed medium rates of leaching (36-46 kg/ha/y). High rates of leaching were estimated from winter cereals following rape/peas, bare soil following cereals and from autumn applications of animal manure on bare soil (71-78 kg/ha/y). Estimates of leaching from soil of 5, 12 and 20% clay were 68, 44 and 26 kg/ha/y, respectively. Leaching was estimated to rise significantly with increasing amounts of applied N.
The model is suitable for general calculations of the effects of crop rotation, soil type and N-application on nitrate leaching from sandy soil to sandy clay loarns in a temperate coastal climate.     

不同水肥管理模式对太湖地区稻田土壤氮素渗漏淋溶的影响

针对当前我国水稻生产中日益严重的水资源短缺及稻田土壤氮素渗漏淋溶引发的面源污染问题,本研究通过设置2种灌溉方式及4个施氮水平的双因子交互试验,探讨了不同水肥处理对稻田土壤氮素渗漏淋溶的影响.结果表明,稻田20 cm处渗漏水中NH+4-N浓度与施氮量呈正相关关系,减少氮肥施用量,可降低2％～35％的NH+4-N浓度,而80 cm处NH+4-N浓度与施氮量无相关关系;稻田20 cm、80 cm处渗漏水中NO3-N浓度均与施氮量呈正相关关系;控制灌溉显著提高了稻田80 cm处渗漏水中NO-3-N浓度,增幅达31％,但由于其水分渗漏量少,NO3-N淋溶量较常规灌溉仍降低16％～ 49％; NO3-N是稻田中氮素渗漏淋溶的主要形式,占氮素渗漏淋溶总量的77％～92％;减氮施肥条件下,NO3-N渗漏淋溶量降低14％～56％.控灌减氮措施可很好地协调产量效益与水体环境效益,是适宜太湖地区的环境友好型水肥管理模式.     

北方旱作条件下玉米施用氮肥对氮吸收和淋溶的影响

实验研究了北方自然降雨情况下,玉米生育期间的氮素淋溶。结果表明,氮肥的施用量对土壤中硝态氮的积累和移动有影响,氮肥施用量超过300kg hm-2时,0～40cm土层硝态氮累积量明显增加,50cm的土层硝态氮的累积达到高峰;50cm以下土壤中硝态氮累积量逐渐降低,100cm土层施肥处理的硝态氮累积量明显高于对照;从经济效益方面分析,氮肥最佳施肥量为200kg hm-2,过量施肥并不能获得高的经济效益;从环境方面分析,氮肥用量超过150kg hm-2就会发生氮素淋溶。     

A modelling study of nitrogen deposited to arable land from the atmosphere and its contribution to nitrate leaching

Abstract. Atmospheric nitrogen (N) makes a significant contribution to the N inputs to agricultural systems and is a major eutrophying and acidifying input to natural and semi-natural ecosystems. We have estimated the nitrogen deposited to arable land at Rothamsted and at two Nitrate Vulnerable Zones (NVZs) in the UK, Lichfield and the River Waveney. Using the SUNDIAL N cycle model calibrated against measured soil mineral N and leaching losses at Rothamsted, we have calculated the contribution of deposited N to nitrate leaching under a range of crops growing on the major soil series in the NVZs. Approximately 44, 46 and 28 kg N/ha per yr are deposited to arable land around Rothamsted and in the Lichfield and Waveney NVZs, respectively. Most of this is dry-deposited in oxidized forms: nitrogen dioxide and nitric acid are the main components, arising mostly from industry, home heating and vehicle emissions. SUNDIAL predicts that current total leaching losses from arable crops average 39 kg N/ha per yr in the Lichfield NVZ anti 22 kg/ha per yr in the Waveney NVZ. Atsmospheric N contributes about 28% of the N leached from arable land in the Lichfield NVZ and 17% in the Waveney NVZ, a very significant amount. There is little variation in total leaching or the atmospheric contribution to it between soil series within each NVZ, but much variation with crop type and the weather: atmospheric N can comprise over 40% of the N leached under spring cereals in some years.     

Bypass flow and leaching of nitrogen in a Kenyan Vertisol at the onset of the growing season

Abstract. Bypass flow and concurrent leaching of nitrogen were studied on a Vertisol in south-western Kenya under rangeland and bare, manually tilled cropland. Showers of 30 mm/hr were simulated, causing bypass flow of 47–62% in rangeland topsoils and 19–49% in cropland topsoils. Volumetric water contents after experimentation increased from 28 to 35% and from 24 to 38%, respectively, for the two land-use types.
In rangeland samples up to 3.4 kg N/ha was found in the leachate of unfertilized soil. With a fertilizer application of 50 kg N/ha, up to 5.7 kg N/ha was lost from a pre-wetted soil, and more than 20 kg N/ha from dry soil. In cropland topsoils up to 2.2 kg N/ha was lost from unfertilized soil, and only up to 2.9 kg N/ha from both dry and prewetted fertilized soil. Although Vertisols are often linked with excess water, the phenomenon of bypass flow can cause water stress to crops in their early growth stages. Nitrogen leaching losses were large from dry grassland, but prewetting helped to decrease them. On intensively cultivated cropland there was little nitrogen leaching; the tilled topsoil was able to retain most of the supplied nitrogen.     

基于土壤氮素平衡的旱地冬小麦监控施氮

提高作物产量,平衡土壤氮素携出,培肥土壤,避免过多肥料氮残留造成淋溶,是旱地作物施氮的主要目标。本研究通过1 m土层硝态氮监控,从土壤氮素的输入和携出平衡计算氮肥用量,并在陕西永寿不同肥力水平的地块上连续2年布置田间试验进行验证。结果表明,与习惯施肥相比,监控施肥的氮肥用量减少41.2%,籽粒平均增产17.0%,氮肥偏生产力平均增加188.3%,产投比平均提高28.9%。监控施肥处理在收获期1 m土层硝态氮残留量平均为37.0 kg/hm2,较习惯施肥（112.1 kg/hm2）降低66.9%。经过降雨集中的夏季休闲期后,监控施肥处理1 m土层的硝态氮平均增加15.4 kg/hm2,习惯施肥则减少27.4 kg/hm2。这说明通过对1 m土层硝态氮的监控,依据土壤养分平衡,计算旱地小麦氮肥用量,可以提高产量,有效减少氮肥投入,降低成本,增加农户收入,提高氮肥效率,减少旱地土壤硝态氮残留和淋溶。     

Nitrate leaching as affected by long-term N fertilization on a coarse sand

Abstract. A field experiment on a coarse sand (1987–92) was conducted with spring barley ( Hordeum vulgare L.), in order to evaluate the effects of increasing N fertilization on nitrate leaching under temperate coastal climate conditions. The N fertilizer levels were 60 and 120 kg N/ha. The experiment was conducted on a 19-year old permanent field trial with continuous spring barley, initiated in 1968, and included treatments with ploughing in autumn or spring, with or without perennial ryegrass ( Lolium perenne L.) as a catch crop undersown in spring. Prior to 1987, the low and high levels of N fertilizer were 70 and 150 kg N/ha, respectively. To calculate nitrate leaching, soil water samples were taken from a depth of 0.8 m using ceramic cups. The average annual nitrate leaching from plots with 60 and 120 kg N/ha was 38 and 52 kg N/ha/y, respectively. The increased leaching associated with increasing fertilizer application was not caused by inorganic N in the soil at harvest, but rather by greater mineralization, mainly in autumn. Growing of a catch crop was relatively more efficient for reducing nitrate leaching than a long-term low fertilizer application. A 50% reduction in N application decreased average yield by 26%, while nitrate leaching decreased by 27%.     

Concentration Profile of Nitrogen and Phosphorus in Leachate of a Paddy Plot during the Rice Cultivation Period in Southern Korea

Abstract

The relationships between nitrogen (N) and phosphorus (P) concentrations in surface flooding water and those in the leachate of various soil depths were monitored, and temporal variation of leaching losses of N and P from a paddy plot during rice cultivation was estimated under the conditions of southern Korea. Even flooded conditions nitrification in subsurface soil was identified, but nitrate concentrations in leachate were less than 10 mg/L, the standard drinking water nitrate concentration set by the World Health Organization (WHO). The NO₃‐N and ortho‐P concentrations in the leachate were generally higher than those in the surface flooding water. Field data implied that leaching losses would not be accurately estimated under the flooded conditions of the paddy field when using the N and P concentrations of surface flooding water and infiltration depth. The leaching losses of NO₃‐N from paddy fields were high immediately after fertilization. The study results suggested that proper fertilization and irrigation strategies are required to reduce leaching losses of NO₃‐N from paddy fields.     

Fate of fertilizer nitrogen applied to grassland. I. Field leaching results

Results are presented from a 3 year investigation into nitrate leaching from isolated 0.4 ha grassland plots fertilized with 250, 500 and 900 kg N ha^?1 a^?1. Cumulative nitrate leaching over the 3 years was equivalent to 1.5%, 5.4% and 16.7% of the fertilizer applied at 250, 500 and 900 kg N ha^?1 rates respectively. Over a whole drainage season, mean nitrate leachate concentrations at 250 kg N ha^?1 did not exceed 4 mgl^?1, although maximum values of 13.3 mgl^?1 were observed. In contrast, at 900 kg N ha^?1, the mean nitrate leachate concentration in two of the years exceeded 90 mgl^?1. Mineral nitrogen balances constructed for the 1979 growing season indicated that leaching at 250 kg N ha^?1 was low because net mineralization of soil organic nitrogen was small, and crop nitrogen uptake almost balanced fertilizer application. Although the pattern of nitrate leaching suggested that by-passing occurred in the movement of water down the soil profile, it was not possible to confirm this using simulation models of leaching. Possible reasons for this, including the occurrence of rapid water flow down gravitationally drained macropores, are discussed.     

Nährstoffauswaschung aus Weinbergsböden an der Mittelmosel

Leaching of plant nutrients from vineyard soils Leaching of plant nutrients particularly of nitrate from vineyard, arable, and forest soils of the Middle-Mosel have been investigated over a two-year period. Nitrate concentration in the leachate of vineyards amounted to an average of 326 mg NO₃/l and was about 10 to 20 times higher than the nitrate concentration in the leachate of arable and forest soils. According to the hydro-dynamic model assumptions on groundwater flow in the slates of the Rhenish Massif, the data obtained for the groundwater recharge (158-180 mm/year as gained in spring) and leaching of nitrate (144 kg N/ha/year) must be considered as minimum values. Hydrodynamic model assumptions suggest nitrate leaching rates of about 200 kg N/ha. Main reasons for the high leaching of nutrients are heavy fertilizer application and high mineralization rates in the vineyard soils favoured by relatively high soil temperatures and a high soil permeability.     

Einfluß von Düngemaßnahmen auf die Stickstoffauswaschung bei mehrjährigem Silomaisanbau

Influence of fertilization on nitrogen leaching after cultivation of maize for silage over four successive seasons In a field trial, nitrogen leaching from soil was determined between February 1983 and May 1986 by analyzing soil water from 50, 80 and 110 cm below the soil surface every 14 days. On a Stagno-gleyic Luvisol, maize after maize was cultivated over four successive seasons. Nitrogen was applied either minerally in spring according to N_min or as a semiliquid cattle manure. The time of application (autumn and/or spring), application rate and use of nitrification inhibitor dicyandiamide (DCD) were varied. Under very low N-fertilization (underground fertilization only), nitrate nitrogen losses by leaching dropped from 100 kg N/ha in the first year to 33 kg N/ha in the 3^rd. Nitrogen leaching from the various treatment plots depended on the maize growth and rainfall conditions. Because of an intensive and long lasting seepage of gravitational water, nitrogen leaching from the root zone ranged from 113 to 208 kg N/ha during the fall and winter seasons of 1983/84 and 1984/85. Under the more balanced infiltration conditions of the leaching period 1985/86, and after a high yield of maize in 1985, losses due to leaching were reduced to values between 69 to 108 kg N/ha. Under these experimental conditions (deliberately high quantities of semiliquid cattle manure; DCD-application in autumn) no reduction in nitrogen losses could be proved due to the addition of dicyandiamide.     

过量施氮对旱地土壤碳、氮及供氮能力的影响

【目的】过量施氮会影响土壤有机碳、氮的组成与数量,进而改变土壤供氮能力,但关于西北旱地长期过量施用氮肥后土壤有机碳、氮及土壤供氮能力变化的研究尚缺乏。本文在长期定位试验的基础上,通过分析不同氮肥水平特别是过量施氮条件下土壤硝态氮,有机碳、氮和微生物量碳、氮的变化,探讨长期过量施氮对土壤有机碳、氮及供氮能力的影响。【方法】长期定位试验位于陕西杨凌西北农林科技大学农作一站。在施磷(P2O5)100kg/hm2的基础上,设5个氮水平,施氮量分别为N 0、80、160、240、320 kg/hm2。重复4次,小区面积40 m2,完全随机区组排列。种植冬小麦品种为小堰22。本文选取其中3处理,以不施氮为对照(N0)、施氮量N 160 kg/hm2为正常施氮(N160),施氮量N 320 kg/hm2为过量施氮(N320),分别于2012年6月小麦收获后和10月下季小麦播前采集土壤样品,进行测定分析。【结果】过量施氮导致下季小麦播前0—300 cm各土层硝态氮含量显著增加,平均由对照的2.8 mg/kg增加到15.5 mg/kg;同时,0—60 cm和0—300 cm土层的硝态氮累积量分别由对照的47.2和108.9 kg/hm2增加到76.5和727.7 kg/hm2。过量施氮也增加了夏闲期间0—300 cm土层土壤有机氮矿化量,由对照的72.4 kg/hm2增加到130.7 kg/hm2。但过量施氮未显著增加土壤的有机碳含量,却显著增加了土壤有机氮含量,过量施氮0—20、20—40 cm土层土壤有机碳分别为9.24和5.39 g/kg,有机氮分别为1.05和0.71 g/kg,较对照增加52.2%和54.3%。同样,过量施氮未显著影响0—20、20—40 cm土层土壤微生物量碳含量,其平均含量分别为253和205 mg/kg,却显著提高了0—20、20—40 cm土层土壤微生物量氮含量,由对照的24.1和7.5 mg/kg提高到43.6和16.1 mg/kg。【结论】过量施氮可以显著增加旱地土壤剖面中的硝态氮累积量、夏闲期氮素矿化量、小麦播前土壤氮素供应量和土壤微生物量氮含量,但对土壤有机碳和微生物量碳没有显著性影响,同时过量施氮增加了土壤硝态氮淋溶风险,故在有机质含量低的黄土高原南部旱地冬小麦种植中不宜施用高量氮肥,以减少土壤氮素残留和农业投入,达到保护环境和培肥土壤的目的。     

施用氮肥对设施红地球葡萄氮素吸收及产量和品质的影响

为给祁连山沿山区设施红地球葡萄氮肥合理施用及产量品质提升提供技术指导。在4年生红地球葡萄大棚内，设置浅施(20 cm)和深施(40 cm)2个施肥深度，低氮(N 180 kg/hm2)、中氮(N 240 kg/hm2)和高氮(N 300 kg/hm2)3个氮素水平，研究氮肥施用对祁连山沿山冷凉区设施红地球葡萄产量、品质及氮素吸收的影响。结果表明，施用深度相同时，氮肥施用量从180 kg/hm2增加到240 kg/hm2，葡萄发育期叶片和叶柄氮含量显著增加；氮肥施用量从240 kg/hm2增加到300 kg/hm2，葡萄发育期叶片和叶柄氮含量变化不显著，但收获期0～100 cm土层硝态氮残留量明显增加。氮肥施用量相同时，随着施用深度的增加，葡萄发育期叶片和叶柄氮含量显著降低，收获期0～100 cm土层硝态氮残留量明显增加。综合考虑葡萄产量、品质、果实发育期叶片和叶柄氮含量，以及收获期0～100 cm土层硝态氮残留量，20 cm的施肥深度和240 kg/hm2的氮肥施用量为本试验条件下祁连山冷凉区设施红地球葡萄较为适宜的氮肥施用方式。     

滇池流域农田土壤氮素流失影响因子研究

本试验采用田间原位模拟降雨并结合多元线性回归(逐步)的统计分析方法,分别在滇池流域的6个点位研究了旱季和雨季农田土壤的理化性质与氮素流失的关系。结果表明:各点位进行的模拟降雨的产流起始时间、产流历时和平均出水速度,在径流和渗漏两种流失方式下差异显著;两次径流试验中,质地为砂质黏壤土的C-2点(大渔乡元宝村)的初始产流强度和平均产流强度均最大。渗漏是氮素流失的主要方式,流失的形态主要是与NO3--N为主。土壤的孔隙度与降雨平均入渗率呈显著正相关,与径流中总氮(TN)和铵态氮(NH4+-N)的流失量呈负相关。0～20 cm的土壤硝态氮含量与地表径流和渗漏中总氮(TN)、硝态氮(NO3--N)的流失量呈极显著的正相关,是影响氮素流失的最重要因子,且0～20 cm土壤有机质含量与氮素的流失量呈正相关,土壤pH、5～20 cm的土壤含水量均与TN及NO3--N的流失量呈负相关。0～5 cm土壤铵态氮与NH4+-N的流失量呈正相关。     

亚热带主要耕作土壤硝态氮淋失特征试验研究

本文选取红壤、水稻土、潮土、黄棕壤和紫色土等我国亚热带地区的主要耕作土壤为研究对象,采用土柱模拟试验,研究了在这些土壤中,氮素累积与硝态氮迁移的动态特征,并对氮素的淋失风险进行了定量评价和预测。结果表明,硝态氮在土壤中的淋失过程可分为两个明显的阶段:高浓度快速降低阶段和低浓度缓慢降低阶段。硝态氮淋失过程存在明显的拐点,该点对应的累积入渗量（拐点入渗量）变化范围为38.1 - 219.7 mm,且随土壤硝态氮含量的增加呈幂函数关系增加,表明随硝态氮含量的增高,其淋失风险呈加速增大的趋势。硝态氮淋失强度随土壤硝态氮含量的增加呈显著的线性变化趋势。初步估测,我国亚热带地区年降水入渗量700 mm和土壤硝态氮累积水平为N 20 mg /kg条件下,表层土壤（0-20cm）的硝态氮年平均淋失量为N 484.9 kg /hm2,土壤间的变异系数（CV）分别为26.5%。土壤硝态氮含量是影响硝态氮淋失强度的决定性因素,其它土壤性质的影响均相对较小,因此,控制土壤氮素累积和化肥施用水平是降低其淋失风险的关键环节。     

施氮对春玉米氮素利用及农田氮素平衡的影响

田间试验研究了玉米对不同土壤氮素供应水平下作物氮素吸收利用、土壤氮素供应以及农田氮素平衡的影响。结果表明,玉米产量随施氮量的增加而显著提高,当施氮量高于N 240 kg/hm2时,产量有减少趋势;氮素当季利用率随施氮量的增加逐渐降低。土壤中硝态氮含量在玉米整个生育时期呈现先迅速下降后缓慢升高的趋势;玉米成熟期,施氮处理的各层土壤中硝态氮含量显著高于不施氮处理,各层硝态氮含量基本随施氮量的增加而升高。适量施氮促进玉米对氮素的吸收和利用,进而提高玉米生物量和产量;过量施氮导致硝态氮在土壤中大量累积,提高了硝态氮淋溶风险。施氮处理显著提高了收获后土壤中残留无机氮(Nmin),土壤残留Nmin随施氮量的增加而增加;当施氮量高于N 240 kg/hm2时,残留Nmin有下降趋势。氮素表观损失随施氮量的增加而增加。在本试验条件下,综合产量、氮肥利用率和土壤硝态氮累积情况考虑,合理施氮量应控制在N 1802~40 kg/hm2左右。     

Nitrogen Dynamics and Losses in Direct‐Drilled Maize Systems

Abstract

The knowledge of nitrogen (N) losses in direct‐drilling agrosystems is essential to develop strategies to increase fertilizer efficiency and to minimize environmental damage. The objectives were i) to quantify the magnitude of N volatilization and leaching simultaneously as affected by different urea fertilization rates and ii) to evaluate the capacity of these specific plant–soil systems to act as a buffer to prevent nitrate leaching. Two experiments were conducted during 2001/02 and 2002/03 growing seasons in Alberti, Argentina. The crop was direct‐drilled maize and the soil a Typic Argiudoll. Ammonia losses, N uptake by crop at flowering and harvest, grain yield, N in previous crop residues, and soil nitrate content up to 2‐m depths were determined. Nitrogen availability, soil nitrate (NO₃)‐N up to 1 m plus fertilizer N, was linearly and highly associated with crop N uptake at flowering (R²=0.93, P<0.01) and at harvest (R²=0.852, P<0.01). Around 17.5% of fertilizer N was lost by volatilization in 10 days. The obtained values of residual nitrate N up to the 150‐cm depth were associated (R²=0.960, P<0.001) with those predicted by the nitrate leaching and economic analysis package (NLEAP) model. Maize in the direct‐drilling system was able to cycle N from the previous crop residues, N from soil organic matter, and N from fertilizers with few losses.     

Nitrate leaching and pasture yields following the application of dairy shed effluent or ammonium fertilizer under spray or flood irrigation: results of a lysimeter study

Abstract. Nitrate leaching and pasture ( Lolium perenne / Trifolium repens ) yields were measured on monolith lysimeters (80 cm diam. × 120 cm depth) of a Templeton sandy loam soil (Udic Ustochrept), following repeated applications of dairy shed effluent (DSE) or ammonium fertilizer (NH₄Cl), under spray (50 mm/month) or flood (100 mm/month) irrigation. Applications of DSE at 400 kg N/ha per annum resulted in significantly less nitrate leaching (8–25 kg N/ha per yr) compared with NH₄Cl (28–48kg N/ha per yr) ( P < 0.01). Over the two year period, the total mineral N (predominantly nitrate) leached was equivalent to 2.5–3.7% of the total N applied in the DSE and 8.7–9.8% of the N applied in the NH₄Cl. There was a trend of slightly less nitrate leaching under the flood irrigation than under the spray irrigation, probably because of the greater potential for denitrification under the wetter conditions. Average nitrate concentrations in the leachate were generally below the drinking water standard except in the NH₄Cl treatment under spray irrigation where it averaged 10 mg NO₃-N/l over the two year period. DSE was equally as effective as NH₄Cl in stimulating pasture dry matter production. Annual nitrogen uptakes were similar for the DSE (343 kg N/ha) and NH₄Cl (332–344kg N/ha) treatments in the first year but were higher in the DSE (361–412 kg N/ha) than in the NH₄Cl (324–340 kg N/ha) treatments in the second year. Pasture uptakes of phosphorus and sulphur were also higher in the DSE than in the NH₄Cl treatments in the second year. The results emphasize the need to set different regulatory limits for land application of organic wastes of various types and for N fertilizers.