中国洞庭湖区稻田土壤氮素淋溶损失的系统研究

A two-year lysimeter study was conducted to study the effects of different fertilizers and soils on nitrogen leaching loss in a double rice cropping system by considering three major types of paddy soils from the Dongting Lake area. The results showed that N concentration in the leachate did not differ significantly among the treatments of urea, controlled release N fertilizer and pig manure and that all these fertilizers produced higher total nitrogen (TN) concentrations in the leachate compared to the case where no fertilizer was applied. The TN leaching loss following urea treatment accounted for 2.28%, 0.66%, and 1.50% of the amount of N applied in the alluvial sandy loamy paddy soil (ASL), purple calcareous clayey paddy soil (PCC), and reddish-yellow loamy paddy soil (RYL), respectively. Higher TN loss was found to be correlated with the increased leachate volume in ASL compared with RYL, and the lowest TN loss was observed in the PCC, in which the lowest leachate volume and TN concentration were observed. Organic N and NH4+ -N were the major forms of N depleted through leachate, accounting for 56.8% and 39.7% of TN losses, respectively. Accordingly, soil-specific fertilization regimens are recommended; in particular, the maximum amount of fertilizer should be optimized for sandy soils with a high infiltration rate. To avoid a high N leaching loss from rice fields, organic N fertilizers such as urea or coated urea should primarily be used for surface topdressing or shallow-layer application and not for deep-layer application.     

中国云南省滇池盆地东南区由于土地利用方式的变化（从水田变为旱地或温室土壤）导致土壤理化性质的变化研究

Paddy fields in the southeastern basin of Dianchi Lake have rapidly changed to greenhouses since 1999. A total of 61 surface soil samples, including 43 greenhouse soils, 12 upland soils, and 6 paddy soils, were collected from a flat lowland area mainly used for agricultural production fields in the southeastern basin of Dianchi Lake. Analyses of the soil samples indicated that the greenhouse soils were characterized by a lower organic matter content, lower pH, and higher soluble nutrients than the paddy soils in the area. The lower organic matter content of the greenhouse soils was ascribed to environmental or management factors rather than the clay content of the soil. Accumulation of soluble nutrients, especially inorganic N, was due to over-application of fertilizers, which also caused soil acidification. The average amount of readily available N, P, and K accumulated in the greenhouse soils was estimated to be equal to or higher than the annual input of these nutrients as a fertilizer, indicating that a reduction in fertilizer application was possible and recommended. In contrast, a very low available Si content was observed in the paddy soils, suggesting the need for Si application for rice production.     

中国亚热带地区土地利用和磷释放的数量关系

The increase of phosphorus concentration is a crucial factor causing the eutrophication of water body.while land use has an important impact on agricultural non-point sources(NPS) phosphorus discharge,Seven sites controlling the water in four sub-watersheds and the main exit of the Meicun Watershed of Xuancheng County,Anhui Provinec,were investigated by dynamic monitoring of stream water and nutrient discharge,integrating interpretation of areial image and GIS analysis to find out how the land use affects phosphorus loss with stream water in typical agriculture-forest watershed in subtropica China.These monitored sites are different in structure of typical agriculture-forest watershed in subtropical China.These monitored sitess are different in structure of land use,Phosphorus concentration of the stream water was analyzed every week and at the next day of rainfall,The velocity of flow was measured by kinemometer to calculate the runoff flux and phosphorus discharge.The results showed that the runoff flux and the discharges of dissolved phosphorus(DP),particle-associated phosphorus(PAP) and total phosphorus(TP) had significant exponential relationships with the area percentages of forest,pond and paddy field.There existed a significant exponential relationships with the area percentages of forest,pond and paddy field.There existed a significant linear relationship between the TP and PAP concentrations in stream water and the area percentages of forest,pond and paddy field,and the discharge of PAP was also significantly linearly correlated with the discharge of suspended soil particles.There was a logarithmic linear relationship between DP and PAP discharges,The study indicated that the adjustment of land used patterns and construction of ecologically sound aldnscape would be an important measure to reduce the runoff discharge of phosphorus,The results would be very useful in building the best management practices(BMPs) of agricultural watershed in subtropics.     

可变电荷与恒电荷稻田土壤硝态氮和铵态氮淋失规律

A variable-charge (VC) and a permanent-charge paddy soil (PC) were selected to study nitrate (NO3--N) and ammonium (NH4+-N) leaching with N isotopes for one consecutive year. An irrigation and intermittent drainage pattern was adopted to mimic natural occurrence of rainfall during the upland crop season and drainage management during the flooded rice season. Treatments to each soil type were no-N controls (CK), 15N-labeled (NH4)2SO4 (NS) and milk vetch (NV) applied at a rate equivalent to 238 kg N ha–1 to unplanted lysimeters, totaling six treatments replicated in triplicates. Results indicated that the soil type dominated N leaching characteristics. In the case of PC, NO3--N accounted for 78% of the total leached inorganic N; NS was prone to leach three times more than the NV, being 8.2% and 2.4% of added 15N respectively; and > 85% of leached NO3--N came from native N in the soil. In the case of VC, NH4+-N made up to 92% of the total inorganic N in leachate. Moreover, NH4+-N leaching was detected throughout the whole incubation, and was particularly high during the flooded season. NO3--N leaching in VC occurred later at a lower rate compared to that in PC. The findings of this study indicate that NO3--N leaching during the drained season in permanent-charge paddy soils and NH4+-N leaching in variable-charge soils deserve more attention for regional environmental control.     

中国南方大棚蔬菜地氮平衡与损失

High rates of fertilizer nitrogen (N) are applied in greenhouse vegetable fields in southeastern China to maximize production;however,the N budgets of such intensive vegetable production remain to be explored.The goal of this study was to determine the annual N balance and loss in a greenhouse vegetable system of annual rotation of tomato,cucumber,and celery at five N (urea) application rates (0,348,522,696,and 870 kg N ha-1 year-1).Total N input to the 0-50 cm soil layer ranged from 531 to 1 053 kg ha-1,and N fertilizer was the main N source,accounting for 66%-83% of the total annual N input.In comparison,irrigation water,wet deposition,and seeds in total accounted for less than 1% of the total N input.The fertilizer N use efficiency was only 18% under the conventional application rate of 870 kg N ha-1 and decreased as the application rate increased from 522 to 870 kg N ha-1.Apparent N losses were 196-201 kg N ha-1,of which 71%-86% was lost by leaching at the application rates of 522-870 kg N ha-1.Thus,leaching was the primary N loss pathway at high N application rates and the amount of N leached was proportional to the N applied during the cucumber season.Moreover,dissolved organic N accounted for 10% of the leached N,whereas NH3 volatilization only contributed 0.1%-0.6% of the apparent N losses under the five N application rates in this greenhouse vegetable system.     

灌区马铃薯-大白菜双季栽培降低土壤硝酸盐淋洗风险并增加资源利用效率的研究

To reduce the nitrate leaching risk after potato (Solanum tuberosum L.) harvest and improve nitrogen fertilizer-use efficiency, a potato-cabbage double cropping system (DCS) was established at Hetao, North China, an arid area with irrigated land. A two-year field experiment demonstrated that planting early-maturing potato cultivar under plastic mulch shortened its growth period by 14 d and allowed a second crop of cabbage to scavenge the soil residual NO 3 -N to a depth of 160 cm, substantially reducing the risk of nitrate leaching into groundwater. The yearly total N uptake in DCS was about 110 kg ha 1 more than that in the conventional cropping system (CCS), i.e., mono potato planting. This accounted for apparent nitrogen recovery (ANR) improvement of 16.90%- 26.57% in the DCS as compared to that in the CCS for both years. As a result, the soil residual NO 3 -N in the 0-160 cm soil profile in the DCS was lower than that in the CCS. The solar energy-use efficiency and soil-use efficiency were also substantially increased with DCS.     

Losses of Urea-Nitrogen Applied to Maize Grown on a Calcareous Fluvo-Aquic Soil in North China Plain

Field experiments were conducted in a maize (Zea mays L.)field of a calcareous fluvo-aquic soil in North China Plain for studying the fate and ammonia loss of urea-N applied at seedling stage,as well as the effectiveness of coated calcium carbide(CCC) in reducing N loss and in improving the yield efficiency of urea.Results show that:(1) For the surface-broadcast treatment ammonia volatilization (measured with micro-meteorological technique)took place quickly,reached the peak 20-26hr after application,and then declined gradually;the cumulative ammonia loss approached the maximum 188hr after application (30% of the N applied),and increased only to 32% 284 hr after application;the latter accounted for 71% of the total loss (45% of applied N).(2) In the case of point placement at a depth of 5-10 cm,ammonia loss 188hr after application was only 12% of the N applied,accounting for 40% of the total loss.(3) There was no difference in total loss between the application depths of 6cm and 10 cm,the loss of them was 30% and 29%,respectively.(4) Total loss of N applied at lower rate (40kg N/ha)with point deep placement at 6cm depth was found only 4% of the N applied,it rose up to 30% when the rate of application increased to 80kg N/ ha.(5) The nitrification inhibitor,CCC,seemed to enhance N loss of urea rather than reduce it,and did not show any benefit effect in improving the yield efficiency of urea,which is presumably due to the high potential of ammonia volatilization in the soil and climatic conditions under investigation.     

中国太湖地区稻麦轮作农田硝态氮动态与氮素平衡

Nitrate-nitrogen (NO 3--N) dynamics and nitrogen (N) budgets in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) rotations in the Taihu Lake region of China were studied to compare the effects of N fertilizer management over a two-year period. The experiment included four N rates for rice and wheat, respectively: N1 (125 and 94 kg N ha-1 ), N2 (225 and 169 kg N ha-1 ), N3 (325 and 244 kg N ha-1 ), and N0 (0 kg N ha-1 ). The results showed that an overlying water layer during the rice growing seasons contributed to moderate concentrations of NO 3--N in sampled waters and the concentrations of NO 3--N only showed a rising trend during the field drying stage. The NO 3--N concentrations in leachates during the wheat seasons were much higher than those during the rice seasons, particularly in the wheat seedling stage. In the wheat seedling stage, the NO 3--N concentrations of leachates were significantly higher in N treatments than in N0 treatment and increased with increasing N rates. As the NO 3--N content (below 2 mg N L-1 ) at a depth of 80 cm during the rice-wheat rotations did not respond to the applied N rates, the high levels of NO 3--N in the groundwater of paddy fields might not be directly related to NO 3--N leaching. Crop growth trends were closely related to variations of NO 3--N in leachates. A reduction in N application rate, especially in the earlier stages of crop growth, and synchronization of the peak of N uptake by the crop with N fertilizer application are key measures to reduce N loss. Above-ground biomass for rice and wheat increased significantly with increasing N rate, but there was no significant difference between N2 and N3. Increasing N rates to the levels greater than N2 not only decreased N use efficiency, but also significantly increased N loss. After two cycles of rice-wheat rotations, the apparent N losses of N1, N2 and N3 amounted to 234, 366 and 579 kg N ha-1 , respectively. With an increase of N rate from N0 to N3, the percentage of N uptake in total N inputs decreased from 63.9% to 46.9%. The apparent N losses during the rice seasons were higher than those during the wheat seasons and were related to precipitation; therefore, the application of fertilizer should take into account climate conditions and avoid application before heavy rainfall.     

Effects of Irrigation Patterns and Nitrogen Fertilization on Rice Yield and Microbial Community Structure in Paddy Soil

Water and nitrogen (N) are considered the most important factors affecting rice production and play vital roles in regulating soil microbial biomass, activity, and community. The effects of irrigation patterns and N fertilizer levels on the soil microbial community structure and yield of paddy rice were investigated in a pot experiment. The experiment was designed with four N levels of 0 (N0), 126 (N1), 157.5 (N2), and 210 kg N ha-1 (N3) under two irrigation patterns of continuous water-logging irrigation (WLI) and water-controlled irrigation (WCI). Phospholipid fatty acid (PLFA) analysis was conducted to track the dynamics of soil microbial communities at tillering, grain-filling, and maturity stages. The results showed that the maximums of grain yield, above-ground biomass, and total N uptake were all obtained in the N2 treatment under WCI. Similar variations in total PLFAs, as well as bacterial and fungal PLFAs, were found, with an increase from the tillering to the grain-filling stage and a decrease at the maturity stage except for actinomycetic PLFAs, which decreased continuously from the tillering to the maturity stage. A shift in composition of the microbial community at different stages of the plant growth was indicated by principal component analysis (PCA), in which the samples at the vegetative stage (tillering stage) were separated from those at the reproductive stage (grain-filling and maturity stages). Soil microbial biomass, measured as total PLFAs, was significantly higher under WCI than that under WLI mainly at the grain-filling stage, whereas the fungal PLFAs detected under WCI were significantly higher than those under WLI at the tillering, grain-filling, and maturity stages. The application of N fertilizer also significantly increased soil microbial biomass and the main microbial groups both under WLI and WCI conditions. The proper combination of irrigation management and N fertilizer level in this study was the N2 (157.5 kg N ha-1) treatment under the water-controlled irrigation pattern.     

华北平原水浇玉米-小麦轮作农田氨挥发与反硝化损失

Ammonia (NH3) volatilization, denitriflcation loss, and nitrous oxide (N2O) emission were investigated from an irrigated wheat-maize rotation field on the North China Plain, and the magnitude of gaseous N loss from denitrification and NH3 volatilization was assessed. The micrometeorological gradient diffusion method in conjunction with a Bowen Ratio system was utilized to measure actual NH3 fluxes over a large area, while the acetylene inhibition technique (intact soil cores) was employed for measurement of denitrification losses and N2O emissions. Ammonia volatilization loss was 26.62% of the applied fertilizer nitrogen (N) under maize, while 0.90% and 15.55% were lost from the wheat field at sowing and topdressing, respectively. The differences in NH3 volatilization between different measurement events may be due to differences between the fertilization methods, and to differences in climatic conditions such as soil temperature. Denitrification losses in the fertilized plots were 0.67%-2.87% and 0.31%-0.49% of the applied fertilizer N under maize and wheat after subtracting those of the controls, respectively. Nitrous oxide emissions in the fertilized plots were approximately 0.08%-0.41% and 0.26%-0.34% of the applied fertilizer N over the maize and wheat seasons after subtracting those of the controls, correspondingly. The fertilizer N losses due to NH3 volatilization were markedly higher than those through denitriflcation and nitrous oxide emissions. These results indicated that NH3 volatilization was an important N transformation in the crop-soil system and was likely to be the major cause of low efficiencies with N fertilizer in the study area. Denitriflcation was not a very important pathway of N fertilizer loss, but did result in important evolution of the greenhouse gas N2O and the effect of N2O emitted from agricultural fields on environment should not be overlooked.     

江川灌区旱田改水田加剧水体氮磷污染

黑龙江省江川灌区实施旱田改水田后,粮食产量持续上升,同时也暴露了以总氮和总磷为主的非点源污染问题。该文在GIS平台的支持下,运用SWAT模型,建立了模型所需的空间数据库和属性数据库,并运用实测资料对模型参数进行了率定。最后,设置了不同的情景,在耕地面积不变的情况下,改变水田比例为现状的70%、50%,从而研究农业非点源污染输出变化。研究表明:水田面积为70%和50%的情况下,月平均径流深比现状减少20.95、41.37 mm,总氮负荷减少27.84、48.16 t/a,总磷负荷减少1.66、2.89 t/a,说明旱田改水田将会对水环境产生不利影响。通过情景模拟发现,减少施肥量和节水灌溉均可以在一定程度上控制污染物输出,施肥量减少50%后,总氮输出减少25.23%,总磷减少16.32%。在实际生产生活中,为保证粮食产量,可以通过改变施肥方式或设置人工湿地等方法减少农业面源污染。     

基于输出系数模型的水库汇水区农业面源污染负荷估算

面源污染是导致环境恶化的主要原因之一,由其所引起的水体富营养化现象,已严重威胁着水环境生态安全。该文以长春市水源地新立城水库汇水区为研究对象,选用输出系数模型对其农业非点源污染负荷进行估算,得到结果如下:1)汇水区内农业非点源污染总氮、总磷负荷量分别为2 822.485、471.123 t/a,且二者空间分布较一致;2)总氮负荷量的贡献率大小顺序为:土地利用畜禽养殖农村人口,总磷的污染负荷贡献率大小为:畜禽养殖土地利用农村人口;3)选取水库2004-2013年水质监测数据计算营养盐输出负荷,与模型估算的输出负荷进行对比,得到模型模拟具有较高精度,系数选取合理可靠,可信度高,可在研究区范围内进行推广,能够为长春市水源地综合整治及水利规划提供了数据支撑及科学依据。     

华南受干扰林和成熟林氮素流失对模拟氮沉降的响应

Current nitrogen (N) leaching losses and their responses to monthly N additions were investigated under a disturbed pine (Pinus massoniana) forest and a mature monsoon broadleaf forest in southern China. N leaching losses from both disturbed and mature forests were quite high (14.6 and 29.2 kg N ha^-1 year^-1, respectively), accounting for 57% and 80% of their corresponding atmospheric N inputs. N leaching losses were substantially increased following the first 1.5 years of N applications in both forests. The average increases induced by the addition of 50 and 100 kg N ha^-1 year^-1 were 36.5 and 24.9 kg N ha^-1 year^-1, respectively, in the mature forest, accounting for 73.0% and 24.9% of the annual amount of N added, and 14.2 and 16.8 kg N ha^-1 year^-1 in the disturbed forest, accounting for 28.4% and 16.8% of the added N. Great N leaching and a fast N leaching response to N additions in the mature forest might result from long-term N accumulation and high ambient N deposition load (greater than 30 kg N ha^-1 year^-1 over the past 15 years), whereas in the disturbed forest, it might result from the human disturbance and high ambient N deposition load. These results suggest that both disturbed and mature forests in the study region may be sensitive to increasing N deposition.     

基于Century模型和1:500 000土壤数据库的华东旱地土壤有机碳动态模拟

Changes in soil organic carbon (SOC) in agricultural soils influence soil quality and greenhouse gas concentrations in the atmosphere. Dry farmland covers more than 70% of the whole cropland area in China and plays an important role in mitigating carbon dioxide (CO2) emissions. In this study, 4109 dry farmland soil polygons were extracted using spatial overlay analysis of the soil layer (1:500000) and the land use layer (1:500000) to support Century model simulations of SOC dynamics for dry farmland in Anhui Province, East China from 1980 to 2008. Considering two field-validation sites, the Century model performed relatively well in modeling SOC dynamics for dry farmland in the province. The simulated results showed that the area-weighted mean soil organic carbon density (SOCD) of dry farmland increased from 18.77 Mg C ha1 in 1980 to 23.99 Mg C ha1 in 2008 with an average sequestration rate of 0.18 Mg C ha1 year?1. Approximately 94.9% of the total dry farmland area sequestered carbon while 5.1% had carbon lost. Over the past 29 years, the net SOC gain in dry farmland soils of the province was 19.37 Tg, with an average sequestration rate of 0.67 Tg C year1. Augmentation of SOC was primarily due to increased consumption of nitrogen fertilizer and farmyard manure. Moreover, SOC dynamics were highly differentiated among dry farmland soil groups. The integration of the Century model with a fine-scale soil database approach could be conveniently utilized as a tool for the accurate simulation of SOC dynamics at the regional scale.     

紫色土丘陵区农业小流域暴雨事件磷素多尺度流失特征

为了揭示自然小流域尺度降雨、地形、土地利用结构等对泥沙和磷素输出的影响,根据丘陵区农业小流域自然地貌与土地利用特征,设计了不同尺度的小流域监测点,分别为苏荣、截流、大兴、万安,监测面积分别为3.0,34.6,480.3,1 236.4hm~2,并选择了降雨侵蚀力(R)分别为1 411.5,595.7,391.4 MJ·mm/(hm~2·h)的3场降雨事件监测小流域内磷素流失过程特征。结果表明:(1)以居民点集镇和耕地为主的苏荣和截流小流域水文响应速度较快,暴雨事件中径流峰值出现在降雨峰值后的5~10min,较大尺度大兴和万安小流域泥沙浓度峰值与径流峰值滞后于降雨峰值0.5~3h。(2)3场暴雨径流中泥沙与全磷、颗粒态磷均存在较一致的显著相关关系(R0.6,P0.01),泥沙、全磷流失负荷在源头小流域(苏荣、截流)最高,3场暴雨苏荣全磷平均流失负荷达到0.36kg/hm~2,万安小流域泥沙、全磷流失负荷最低,全磷平均流失负荷为0.009kg/hm~2。(3)小流域径流中颗粒态磷占全磷流失量50%以上。(4)多元回归分析结果表明,径流量和泥沙含量可用于进行磷素流失通量预测。坡耕地、林地与水田带状组合结构可显著降低小流域泥沙和磷素流失负荷。研究结果为计算丘陵区农业小流域暴雨过程中磷素多尺度流失负荷提供参考。     

亚热带小流域土壤氮磷分布及其环境效应

土壤氮磷积累是引起农业面源污染的主要原因。为探讨土壤氮磷含量的分布状况及其对环境的影响,选取位于长沙县金井镇的小流域为研究区域,以表层土壤(0-20cm)为采样对象,按不同的土地利用方式共采集样品1 118个。以土地利用类型为分析单元,分析说明了土壤全氮、全磷的分布特征及其环境效应。结果表明:土壤全氮和全磷含量的平均值分别为1.66,0.54g/kg,变异系数分别为34.9%和46.3%,均属于中等变异。菜地土壤全氮含量主要分布在1.8～2.4g/kg区间,旱地和水田为1.2～1.8g/kg,林地和茶园为0.6～1.2g/kg;菜地土壤全磷含量主要分布在大于1.0g/kg区间,旱地为0.6～0.8g/kg,水田为0.4～0.6g/kg,林地和茶园为0.2～0.4g/kg。结合地下水氮磷含量分析表明,土壤氮素含量与地下水铵态氮含量增加有关,对地下水水质产生影响,其中水田的影响尤为突出;土壤磷素的淋失可能具有季节性差异,还有待进一步验证。     

南亚热带三种不同土地利用历史的森林生态系统土壤可交换阳离子对模拟氮沉降的响应

The effects of simulated nitrogen (N)deposition on soil exchangeable cations were studied in three forest types of subtropical China. Four N treatments with three replications were designed for the monsoon evergreen broadleaf forest (mature forest):control (0 kg N ha^-1 year^-1), low N (50 kg N ha^-1 year^-1), medium N (100 kg N ha^-1 year^-1)and high N (150 kg N ha^-1 year^-1), and only three treatments (i.e., control, low N, medium N)were established for the pine and mixed forests. Nitrogen had been applied continuously for 26 months before the measurement. The mature forest responded more rapidly and intensively to N additions than the pine and mixed forests, and exhibited some significant negative symptoms, e.g., soil acidification, Al mobilization and leaching of base cations from soil. The pine and mixed forests responded slowly to N additions and exhibited no significant response of soil cations. Response of soil exchangeable cations to N deposition varied in the forests of subtropical China, depending on soil N status and land-use history.     

Effect of Simulated N Deposition on Soil Exchangeable Cations in Three Forest Types of Subtropical China

The effects of simulated nitrogen (N) deposition on soil exchangeable cations were studied in three forest types of subtropical China.Four N treatments with three replications were designed for the monsoon evergreen broadleaf forest (mature forest):control (0 kg N ha-1 year-1),low N (50 kg N ha-1 year-1),medium N (100 kg N ha-1 year-1) and high N (150 kg N ha-1 ycar-1),and only three treatments (i.e.,control,low N,medium N) were established for the pine and mixed forests.Nitrogen had been applied continuously for 26 months before the measurement.The mature forest responded more rapidly and intensively to N additions than the pine and mixed forests,and exhibited some significant negative symptoms,e.g.,soil acidification,Al mobilization and leaching of base cations from soil.The pine and mixed forests responded slowly to N additions and exhibited no significant response of soil cations.Response of soil exchangeable cations to N deposition varied in the forests of subtropical China,depending on soil N status and land-nse history.     

沿海酸性硫酸盐土中气态N损失的短期研究

NO x and N 2 O emissions from coastal acid sulfate soils (CASS) cultivated for sugarcane production were investigated on the coastal lowlands of northern New South Wales,Australia.Two series of short-term measurements were made using chambers and micrometeorological techniques.Series 1 occurred during the wet season,the water-filled pore space (WFPS) was between 60%-80% and the site flooded during the measurements.Measurements were made directly after the harvest of soybean crop,which fixed an estimated 100 kg N ha-1,and the emission amounted to 3.2 kg NO x-N ha-1 (12 d) and 1.8 kg N 2 O-N ha-1 (5 d).Series 2 was made towards the end of the dry season when the WFPS was less than 60%.In Series 2,after an application of 50 kg N ha 1,emissions were markedly less,amounting to 0.9 kg N ha-1 over 10 d.During both series when the soil was moist,emissions of NO x were larger than those of N 2 O.The emission of NO x appeared to be haphazard,with little time dependence,but there was a clear diurnal cycle for N 2 O,emphasising the need for continuous measurement procedures for both gases.These results suggest that agricultural production on CASS could be important sources of greenhouse gases and nitrogen practices will need to be optimised to reduce the offsite effects of atmospheric warming,acidification or nitrification.Many questions still remain unanswered such as the emissions during the soybean bean filling stage and crop residue decomposition,the longer-term losses following the fertiliser application and emissions from CASS under different land uses.