Simulation of Nitrogen and Phosphorus Transport and Transformation in Saturated-Unsaturated Soil

Nitrogen-2D is a physically-based model developed on the basis of SWMS-2D to predict the fate of nitrogen and phosphorus following irrigation with effluent.To test the model, a sewage effluent irrigation experiment was conducted.In this paper, the nitrogen-2D model is extended and tested with data from four effluent-irrigated winter wheat plantations.The results show that, on the whole, measured and simulated values are in reasonably good agreement, especially soil water content and soil ammonia content, which indicates that it can offer reliable prediction of the fate of water and nitrogen in spite of the relative simplicity of the model.The model is then used to estimate the soil nitrogen and phosphorus behavior in winter wheat field under the same situation with different concentrations of nitrogen and phosphorus in the sewage effluent.The results show that under the simulated conditions, no nitrogen or phosphorus leaching happened at 1.5 m depth in the period, and because of the strong adsorbability of the soil, 49% of the ammonia following irrigation with effluent was turned into nitrate by nitration instead of uptake.Denitrification of nitrate is the major channel resulting in loss of soil nitrogen fertilizer with a volume of about 12.6% of the input nitrogen.Nitrate is much more available for crop than ammonia and the current fertilization utilization rate is 23.3%.