Nitrate Accumulation, Leaching,Runoff And Oxide Emissions In Agricultural Soil Of China

Nitrogen cycling and environmental effect of farmland ecological system is an important part ofthe global nitrogen cycle, The evaluation of soil nitrate nitrogen accumulation, leaching, runoff loss andnitrous oxide emissions, analyze its influence factors, coud providie a theoretical basis for enhancingnitrogen management and reducing air and water pollution. In this study, the relevant research data onfarmland soil nitrate accumulation, leaching, runoff losses and nitrous oxide emissions during1980-2011were collected. Soil nitrate accumulation, leaching and runoff losses status quo was analyzedand summarized by use of statistical methods in agricultural soil of China. Emission factor of nitrousoxide emissions was summarized through the Meta Analysis method. The rate of nitrous oxideemissions was estimated by combining the summarized emission factor with IPCC2006Tier2method.The main results were presented as the following:（1）The average of the0-100cm soil nitrate accumulation reached to103.38kgN/hm2in agriculturalsoil of China. The average of soil nitrate accumulation in North and south of the Yangtze River was120.01and133.32kgN/hm2respectively, slightly higher than the national average. The soil nitrateaccumulation in Northwest and Northeast region was81.18and32.22kg N/hm2respectively, whichwere below the national level. The nitrate accumulation in northeast region accumulation was only31%of the national average accumulation, significantly lower than the other three regions. The average soilnitrate accumulation was132,481and781kgN/hm2in daejeon, vegetable fields and orchardsrespectively. The average soil nitrate accumulation was only127and162kgN/hm2on wheat and cornrespectively. The average soil nitrate accumulation of vegetables in open field and greenhousevegetables reached468and589kgN/hm2respectively, it is much higher than that of wheat and corn.（2）An unpward trend in soil nitrate accumulation of farmland system was showed in the past decade,from338.9kgN/hm2in2000to216.8kgN/hm2in2011, an annually average5.1%increse. It wasshowed a significiantly positive correlation between soil nitrate accumulation and nitrogen applicationrate and the correlation coefficient r, was0.5558**. A quadratic function highly significant correlationwas showed between rainfall and soil nitrate accumulation and the correlation coefficient r, was0.6116**. Soil nitrate accumulation was maximum when rainfall was between500and550mm. Amultiple regression model between soil nitrate accumulation and nitrogen rate, railfall was set up.（3）The value of soil N2O background emissions in the paddy field and in upland was0.78kgN/hm2 and0.76kgN/hm2respectively in China Soil N2O background emissions of wheat, corn, rice andvegetable fields were0.91,0.47,0.78and0.68kgN/hm2respectively and a regressive trend of wheat,rice, vegetables, corn was showed. It was showed that N2O emission factor in paddy fields and inupland was0.42%and0.64%respectively. As far as different regions were concerned N2O emissionfactors was to1.46%in the northeast, followed by0.92%in the southwest,0.77%in the northwest, andthe minimum was only0.26%in South China. As far as different agrotypes were concerned paddy soilnitrous oxide emission factor was minimum, only0.42%while the vegetable field emission factor up to0.79%.（4）It was showed an increasing trend in N2O emissions in agricultural soil of China from1980to2011,an average annual increased of3.8%from99.3Gg to220.5Gg. The average annual increase was5.2%from69.1Gg to184.86Gg in upland while little change but a growing trend in recent years wasshowed in paddy fields. As far as provincial areas were concerned the highest N2O emissions of unitarea was Beijing, up to6.01kgN/hm2, and the lowest was Heilongjiang, only0.86kgN/hm2. The N2Oemissions of unit in Hebei Province was4.27kgN/hm2, ranked seventh in China. A significant linearpositive correlation was showed between paddy fields as well as upland N2O emissions (remove thebackground value removed) and nitrogen application rate, the correlation coefficients r were0.5538**and0.5096**respectively. The ratio of soil carbon and nitrogen could also affect N2O emissions, whencarbon and nitrogen ratio increased, N2O emissions reduced. By use of the regression method, a modelbewteen N2O emissions (Y) and N-N application rate, P-average precipitation, Q-soil total nitrogen,T-average temperature could be establishend as the following: Y=(2.418+0.001N+0P-0.103Q+0.022T）3.（5）Among Under different cropping systems the average soil nitrate leaching in the vegetable washighest. Soil nitrate leaching on greenhouse vegetable open field vegetable, wheat, corn and rice was105.44,60.59,47.21,47.19,38.78kgN/hm2respectively. A highly significant linear correlation wasshowed between different stages of nitrogen application rate and nitrate leaching, the correlationcoefficients was r=0.9544**. A binomial correlation was showed between soil nitrate leaching andrainfall, the correlation coefficients was r=0.9772**. The soil nitrate leaching was maximum whenprecipitation reached between600and800mm.（6）Nitrate runoff accounted for94.2%under10kgN/hm2of the global nitrogen cycle in China and theaverage runoff was3.24kgN/hm2. Nitrate runoff from vegetable was much higher than the daejeon.Nitrate runoff of vegetable fields was4.84kgN/hm2in Southern and7.24kgN/hm2in Northernrespecitvely while nitrate runoff of daejeon was1.21kgN/hm2in Southern and1.74kgN/hm2inNorthern respecitvely. The average runoff in North region is higher than the South. A significantly indexpositive correlation was showed between nitrate runoff and nitrogen application rate, the correlationcoefficients was r=0.2522**. A highly significant positive linear correlation was showed between nitraterunoff and rainfall, the correlation coefficients was r=0.4293**.