Characteristics And Contribution Of Nitrogen And Phosphorus Loss In Paddy Runoff With Chemical Fertilizer

In order to obtain high-yield crops and maintain soil fertility,fertilizer was widely used in agricultural production.However,due to the irrational application and low utilization rate of fertilizer,it not only led to a large loss of nitrogen and phosphorus as well as a waste of resources,but it also had an adverse impact on the surrounding environment.So as to explore the characteristics of nitrogen and phosphorus loss in soil overflow and seepage as well as finally estimating the loss after applying chemical fertilizer in paddy soil,this study explored the effect of fertilizer type,the amount of fertilizer and fertilizer application method as well as rainfall intensity in a way combining artificial rainfall simulation experiment with field experiment.The detailed information on research results as following:Firstly,this study explored that fertilizer types affect nitrogen and phosphorus losses by paddy soil overflow and seepage.The detailed information includes:（1）Compared with urea and compound fertilizer,the total loss of TN（Total nitrogen）,NH₄⁺-N（Ammonium nitrogen）and NO₃^--N（Nitrate nitrogen）in soil overflow are the highest for ammonium bicarbonate application,while the smallest for urea and intermediate for compound fertilizer.Compared with calcium superphosphate and compound fertilizer,the total loss of TP（Total phosphorus）is highest after application of potassium dihydrogen phosphate,secondary as compound fertilizer,minimum as calcium superphosphate.（2）Compared with compound fertilizer and ammonium bicarbonate,the total loss of TN,NH₄⁺-N and NO₃^--N in soil seepage after urea application is the largest,while the smallest for ammonium bicarbonate and intermediate for compound fertilizer.The three fertilizers of potassium dihydrogen phosphate,compound fertilizer and superphosphate were applied to the soil respectively,the maximum amount of TP loss in soil seepage is potassium dihydrogen phosphate,followed by compound fertilizer and superphosphate.Based on the above results,Urea and calcium superphosphate are selected as nitrogen and phosphorus fertilizers in the following chapters.Secondly,the amount of fertilizer and fertilizer application method affect nitrogen and phosphorus losses by paddy soil overflow and seepage.The related information is as following:（1）Under the two fertilization methods,the total loss of TN,NH₄⁺-N and NO₃^--N in soil overflow and seepage increases as the fertilizer was increased.（2）Under the same fertilizer level,the amount of nitrogen loss in soil overflow and seepage by scattering fertilizer is the largest,which by mixed fertilizer and soil is behind.Thirdly,rainfall intensity affects nitrogen and phosphorus losses by paddy soil overflow and seepage.The detailed information includes:（1）Under different rainfall intensity,The total loss of TN,NH₄⁺-N,NO₃^--N and TP in soil overflow and seepage increases with the rainfall intensity.（2）Under the same rainfall intensity,The total loss of TN,NH₄⁺-N,NO₃^--N and TP is the largest in the soil overflow,followed by seepage.Therefore,rainfall overflow is the main way of nitrogen and phosphorus loss.Finally,the effect of fertilizer application on nitrogen and phosphorus runoff loss in paddy field was investigated in this study,meanwhile the loss amount was finally estimated.The related information is as following:（1）In the four experiment groups as T0,T1,T2 and T3,the total losses of TN,NH₄⁺-N,NO₃^--N and TP in runoff are 15.74 kg/hm~2,9.05 kg/hm~2,2.17 kg/hm~2 and 0.813 kg/hm~2 respectively.Therefore,nitrogen is the main nutrient loss in runoff,in which NH₄⁺-N plays the main form.（2）The amount of fertilizer application can significantly affect the amount of nitrogen loss in runoff,moreover,there is an obvious linear positive correlation between the amount of nitrogen application and the total loss of TN,NH₄⁺-N and NO₃^--N in runoff.（3）Fertilizer application can significantly improve rice yield,but with fertilizer application levels increased continuously,the rice yield does not continue to improve.Therefore,rational application of fertilizer is the key to improve rice yield and reduce farmland pollution.By investigating the effects of fertilizer type,the amount of fertilizer and fertilizer application method as well as rainfall intensity on nitrogen and phosphorus loss,the study can provide technical support for eutrophication control and retracing agricultural non-point pollution in Sichuan.