Studies On The Regional Model For Water And Nitrogen Management

Computer simulation models are widely used in studies to address the problem that agriculture has been increasingly identified as the largest contributor of non-point source (NPS) pollution of N and P to surface water, groundwater and atmosphere. In this paper, a GIS-based water and N management model (WNMM) was demonstrated to simulate dynamic soil water movement and soil-crop N cycling under a given agricultural management, for the purpose of identifying the best agricultural practices under intensive cropping systems for Fengqiu County in the Huang-Huai-Hai Plain.The main results are as follows:1. Based on site-experiment, soil water deep drainage and nitrate leaching in representative soil (yellow fluvo-aquic soil and Aeolian sandy soil) in Huang-Huai-Hai Plain were simulated with HYDRUS-1D model. Numerical simulation indicated: under conventional water and nitrogen management, soil water deep drainage and nitrate N leaching were very serious. Excess application of irrigated water and N fertilizer was the main cause of soil water deep leakage and nitrate-N loss with leachate. The water leakage amount and nitrate N leaching amount of Aeolian sandy soil were more than that of yellow fluvo-aquic soils, which was significantly to depend on different hydraulic properties of two soil types.2. Twenty-five observing points were sampled in Fengqiu County. The depth of groundwater, nitrate content of groundwater were measured. The geostatistics theory was applied to analyze the data. The results were indicated that the depth of groundwater showed a normal distribution, and the nitrate content showed a lognormal distribution. The rational sampling number was determined in a given precision at a known confidence level. Those observations were correlated in a given spatial range with the semivariance analysis. The Kriging method was applied to estimate the unobserved points and generate the spatial distribution map. These results showed some merit in rational using the groundwater resource and preventing the nitrate pollution.3. Six agricultural scenarios were applied to run WNMM to simulate the behavior ofsoil-crop systems in Fengqiu County in 2001-2002 for identifying the optimal agricultural practices or BMPs. The results showed that the individual soil scenario(scenarios 4) provided the best agricultural practices for 2001-2002 in Fengqiu County, because it could increase crop yield, IWUE and FNUE by 11%, 25% and 143%, respectively, and decrease NH3 volatilisation, denitrification and N2O emission by 80%, 64% and 62%, respectively. The individual soil texture scenario (scenario 6) was the second, and scenario 5 the third, Therefore, the schedules of fertiliser N application and irrigation in Fengqiu County should be changed for achieving high performance of the agricultural ecosystem. On the contrary, the survey scenario (scenario 1) was the worst options and failed to be the best agricultural scenario because of over-irrigation and over-input of fertiliser N application, which caused many environmental problems.