[Simulating soil water drainage and nitrogen leaching in Tianranwenyanqu Basin]

Soil water drainage and nitrogen leaching in Tianranwenyanqu Basin was simulated using DNDC model. The model was validated by data of the water and nitrogen controlling experiment in the basin. The correlation coefficients between simulated and measured values of daily 1 m soil water storage,lower boundary NO3(-) -N concentration, soil water drainage and nitrogen leaching were 0.94 (n = 40), 0.66 (n = 49), 0.89 (n =40), 0.94 (n = 39); and RMSEs were 15.66 mm, 2.66 mg x kg(-1), 9.00 mm, 0.94 kg x hm(-2), respectively. The validated model was then used to simulate soil water drainage and nitrogen leaching in the basin. The results show that, under multi-year average climate and conventional management condition, annual soil water drainage and nitrogen leaching of winter-wheat and summer-corn rotation fields in this basin were 220-327 mm and 73.1-100.6 kg x hm(-2), respectively. The distribution of water drainage and nitrogen leaching were uneven in time and space, leaching happened mainly after fertilization, irrigation or heavy rainfall, and sandy soil regions were the most serious nitrogen leaching area. Unreasonable irrigation, fertilization and poor water and fertilizer preserving capability of the soils,were the major causes of soil water drainage and nitrogen leaching.