[Response of Nitrogen Loss Flux in Purple Soil Sloping Field to Reduced Fertilizer and Combining Straw].

The purple soil sloping field is considered as the main source of sediment and non-point source pollution in the Three Gorges Reservoir area. To prevent and control the non-point source pollution, it is indispensable to explore the characteristics of nitrogen loss in the overland flow and interflow of purple soil sloping field in Three Gorges Reservoir area. The purple soil sloping runoff plots, located in the Shibaozhai Experimental Station of Chengdu Institute of Chinese Academy of Sciences in Zhongxian County, Chongqing, were studied. The experiment included no fertilization treatment (CK), traditional fertilization treatment (T), amended fertilization treatment (T), and reduced fertilizer with straw treatment (T). According to the data of volume of the interflow and runoff and the leach concentration and flux of nitrogen forms under rapeseed-maize rotation system, the response of nitrogen leaching flux to reduce fertilizer with straw application can be definite in purple soil sloping plots. The results show that the ratio of interflow to total runoff is 60.14%-88.56%, and the flux of nitrogen leaching in the interflow accounts for 72.88%-92.35% of total nitrogen loss flux. Ammonium was mainly leached by the overland flow. In addition, nitrate was mainly leached by the interflow and was the main form of nitrogen leaching. The fluxes of ammonium and nitrate under different treatments followed the order T > T > T > CK. The total nitrogen flux of T was 20.07 kg·(hm·a), which was 43.59% and 39.55% lower than that of T and T, respectively. The reduced fertilizer with straw application significantly decreased the leaching flux of ammonium, nitrate, and total nitrogen, and weakened the effect on runoff nitrogen leaching in the purple soil sloping plots.