Applicability Of DSSAT Model To Simulate Rice Growth And Nitrate Leaching In Chao Lake

As an important part of human’s life, underground water provides high quality fresh water for human living. During the economy quickly developing period, environmental system has been seriously contaminated and damaged in China. Particularly, underground water has been serious contaminated by nitrate leaching. When the farmland flooded or a heavy rainfall happened, the nitrate leaching will be highly increased and the nitrogen concentration of underground water will be very high. Especially, if the nitrogen fertilizer over fertilized in farmland, the contamination situation will get worse. Recently, a lot of attentions are focused on nitrogen fertilizer over fertilized in agricultural production, and caused the nitrate contamination in underground water.The experimental site is located in Tongyang Town, Chaohu city. This experimental site is used to study the agricultural non-point source pollution. The single rice-growth is chose as the study object in this article. This research is based on the experimental data and simulation data. Using DSSAT 4.5 model to simulate, outputs simulated rice top yield、simulated grain yield and simulated grain N. Compared the experimental data and simulation data, calculate the parameters which evaluate the simulation results of model. Output and analysis the water content simulations、the nitrate content simulations、the cumulative nitrate leaching 、 the cumulative nitrification and the cumulative denitrification. Use the simulation data and experimental date to study the nitrate leaching risk of different N fertilizer levels. There are six different levels which are N0(N blank fertilizer)、N1(75% N fertilizer)、N2(100% N fertilizer)、 N3(125% N fertilizer)、N4(150% N fertilizer)、N5(200% N fertilizer).The results show:(1) Compared the rice top yield simulations、the rice grain yield simulations and the rice grain N content simulations of N0、N1、N2、N3、N4 and N5 with experimental data, the simulated parameters data NRMSE、R2 and α are about 0.01%-9.50% 、0.948-0.988 and 0.911-1.064. The DSSAT 4.5 model works well according to the results of simulated parameters;(2) The experimental rice top yield and grain yield of N3 are maximum which are 13405kg/ha and 7055kg/ha; the order of the experimental rice top yield and grain yield both are N3>N4>N2>N5>N1>N0;(3) The simulated rice top yield and grain yield of N5 are maximum which are 13972kg/ha and 6715kg/ha; the order of rice top yield simulations and grain yield simulations both are N5>N3>N4>N2>N1>N0;(4) The experimental and simulated rice grain N content of N5 both are maximum which are 124.5kg/ha and 121.4kg/ha, the orders of each both are N5>N3>N4>N2>N1>N0;(5) The results of water content simulations of each layers、nitrate content simulations of each layers in different N fertilizer levels and the cumulative nitrification in different N fertilizer levels show: I、the more N fertilizer input, the cumulative nitrification will be higher; range will be 100.82-198.87kg/ha; the cumulative nitrification of first N fertilized> second> third; II、the paddy soil was flooded during the whole rice growth period, the soil water content was very high, and the soil nitrate content was increased to top value within 3 days after N fertilized then felt down; the risk of nitrate leaching was very high within 5 days after N fertilized; III、the more N fertilizer input, the risk of nitrate leaching will be higher;(6) In different N fertilizer levels, the experimental volumes of nitrate leaching were 0.332kg/ha、0.314kg/ha、0.373kg/ha、0.455kg/ha、0.451kg/ha and 0.700 kg/ha, and showed N5>N3>N4>N2>N0>N1; the simulated experimental volumes of nitrate leaching were 1.72kg/ha 、 1.71kg/ha 、 1.79kg/ha 、 1.86kg/ha 、 1.93kg/ha and1.89kg/ha, and showed N4>N5>N3>N2>N0>N1; the experimental and simulation results both showed the volume of nitrate leaching will be increased first by the more N fertilizer input, then will be decrease by continue to increase N fertilizer input.