Comparison of nitrogen losses by runoff from two different cultivating patterns in sloping farmland with yellow soil during maize growth in Southwest China

The loss of N in farmland is an important cause of agricultural non-point source pollution, which seriously impacts the aquatic environment. A two-year (2017-2018) experiment was conducted to investigate the characteristics of runoff and N losses under different tillage practices. Taking downslope ridge planting and cross ridge planting as the experimental treatments, the characteristics of surface runoff, interflow, and N losses in sloping farmlands with yellow soil were studied throughout the maize growth period. As the rainfall increased, the surface runoff and interflow also increased. The surface runoff and N losses in the surface runoff of downslope ridge planting were significantly higher than those of cross ridge planting. The interflow volumes and N losses in the 0-20 and 20-40 cm soil layers of the cross ridge planting were significantly higher than those of the downslope ridge planting. The total N (TN) losses from surface runoff accounted for 54.95-81.25% of the N losses from all pathways. Therefore, we inferred that surface runoff is the main pathway of N losses. Dissolved total N (DTN) was the main form of N loss under different tillage measures, as it accounted for 55.82-94.41% of the TN losses, and dissolved organic N accounted for 52.81-87.06% of the DTN losses. Thus, we inferred that dissolved N is the main form of N loss. Future research must focus on the prevention and control of the N losses during the maize seedling stage to reduce the environmental pollution caused by ammonium N through runoff.