Effects of mixed grass strip on controlling nitrogen and phosphorus loss of slope land in water source region

Nitrogen and phosphorus loss of slope land is the main pollution resource of lake and reservoir drinking source region. In order to reduce the impact of water and soil erosion of sloping fields on the eutrophication of water and improve sustainability of fragile slopes, the field experiment was conducted in Kunming，Yunnan Province in 2011, where Yunlong reservoir is the largest city centralized drinking resource region of Kunming. And effects of different mixed grass strip treatments on reducing nitrogen and phosphorus losses in slope land of red soil were analyzed. Four treatments, including perennial ryegrass + alfalfa (A), perennial ryegrass+trifolium repens (B), natural vegetation(C) and without grass strip(CK), were designed with three replications in the slopes with 15°. The zone of grass strip standard was 3m*1m and sow seeding rate planted at the upper of slope land of each plot was 10 g/m2. Runoff and sediment were collected during maize growing season from May to October). Results showed that runoff and soil erosion of different grass strip treatments were lower than that of the contrast. The surface runoff and soil control effects of different grass strip were presented a trend of A>B>C>CK, and the control effects of soil erosion were better than those of surface runoff. Compared with CK, A and B decreased the runoff rate by 35.19% and 46.26%, and the erode rate decreased by 73.51%and 78.13%, respectively. N existed in the runoff of slope land was mainly in the form of silt N, which accounted for 80%～85%. P existed in the runoff was mainly in the form of granular P, which accounted for 90%-95%. The effects of different grass strip on preventing N and P loss were：A>B>C>CK. The control effects of total nitrogen loss were better than those of total phosphorus. Compared with CK, B decreased total N and P in runoff by 59.96% and 48.57%, A decreased by 63.31% and 56.91% and C decreased by 29.46% and 26.03%, respectively. This research provides scientific basis for soil erosion and water quality protection.