Nitrogen Percolation Simulation under Sewage Irrigation and Irrigation Pattern Optimization of Typical Area in North Canal Basin

Abstract：In order to reveal the characteristics of the farmland nitrogen percolation of the North Canal Basin, and provide some guidance for the basin＇s general planning of water resources and comprehensive control of non-point source pollution, the improved SWAT model was applied to simulate the characteristics of the farmland nitrogen percolation under sixteen different irrigation patterns in the Wuqing area in the North Canal Basin. The simulation results indicated that the amount of nitrogen percolation increases cor- respondingly with the increase of the sewage irrigation, which is inconspicuous when sewage irrigation less than thrice; While with the same number of the sewage irrigation and under the case of continuous or short time-interval sewage irrigation9 the amount of the nitrogen percolation is relatively larger. And the amount of the nitrogen percolation is relatively smaller if irrigating sewage in the returning green stage or the jointing stage, of the winter wheat, or in the tasseling stage of the summer maize. Besides, the rainfall and irrigation amount are the key factors determining whether the NO3^- --N leaches and the leaching amount, and in the absence of adequate rainfall recharging the soil water storage, a proper irrigation amount would not cause excessive water percolation and NO3^--N leaching loss. The proper irrigation pattern of the Wuqing area is irrigating sewage in the returning green stage or the jointing stage of the winter wheat, while irrigating clean water in the rest growth stages, and irrigating sewage in the tasseling stage of the summer maize.