[Effect of Fertilizer Reduction and Biochar Application on Soil Nitrogen Loss in Purple Upland]

This study seeks to clarify the effect of biochar application on nitrogen loss patterns and flux in purple arid sloping land, so as to provide a scientific basis for improving the quality of farmland and reducing the risk of agricultural non-point source pollution in purple arid sloping land. The effects of four treatments on surface runoff and soil nitrogen loss patterns and fluxes in purple arid sloping land were studied by field experiments, including no fertilization (control), conventional fertilization, optimized fertilization, and biochar (fertilizer reduction and biochar application). The results showed that:① Of the fertilization treatments, the total runoff of conventional treatment was the highest at 16133 L·a^-1, and the total runoff of biochar treatment was the lowest at 11893 L·a^-1. In each fertilization treatment, soil midstream was the main mode of runoff, accounting for 61.80%-68.60% of the total loss. Compared with the control (no fertilization treatment), the sediment loss in other fertilization treatments was decreased, with conventional treatment showing the most significant effect. ② Ammonium nitrogen is mainly lost by surface runoff, accounting for 86.51%-96.58% of the total loss flux. Biochar treatment had the highest loss flux at 0.69 kg·(hm²·a)^-1, and the control treatment had the lowest at 0.17 kg·(hm²·a)^-1. ③ The concentration of granular nitrogen in the production flow of each fertilization treatment was higher than that of the control treatment, and the loss flux of granular nitrogen in the conventional fertilization treatment was the highest at 2.87 kg·(hm²·a)^-1. ④ There was a significant positive correlation between total nitrogen concentration and nitrate nitrogen concentration in the soil midstream and surface runoff of each fertilization treatment (P<0.01). Nitrate nitrogen is the main form of total nitrogen loss, and both take soil midstream as the main way of loss. The total nitrogen loss through soil flow accounted for 72.86%-89.13%, and that of conventional fertilization was the highest at 35.58 kg·(hm²·a)^-1, whereas that of biochar treatment was the lowest at 21.49 kg·(hm²·a)^-1. Reducing the amount of fertilizer and applying biochar can significantly reduce the runoff and nitrogen flux, and effectively prevent and control the risk of agricultural non-point source pollution.