Response of nutrient loss to natural erosive rainfall events under typical tillage practices of contour ridge system in the rocky mountain areas of Northern China.

Abstract

Changes in natural rainfall characterized by heavy precipitation and high rainfall intensity would increase the risks and uncertainty of nutrients losses. Losses of nitrogen (N) and phosphorus (P) with water erosion from agriculture-related activities has become the principal nutrients resulting the eutrophication of water bodies. However, a little attention has been paid to the loss characteristic of N and P responding to natural rainfall in widely used contour ridge systems. To explore the loss mechanism of N and P in contour ridge system, nutrient loss associated with runoff and sediment yield was observed in in situ runoff plots of sweet potato (SP) and peanut (PT) contour ridges under natural rainfall. Rainfall events were divided into light rain, moderate rain, heavy rain, rainstorm, large rainstorm, and extreme rainstorm level, and rainfall characteristics for each rainfall level were recorded. Results showed that rainstorm, accounting for 46.27% of the total precipitation, played a destructive role in inducing runoff, sediment yield, and nutrient loss. The average contribution of rainstorm to sediment yield (52.30%) was higher than that to runoff production (38.06%). Rainstorm respectively generated 43.65-44.05% of N loss and 40.71-52.42% of P loss, although light rain induced the greatest enrichment value for total nitrogen (TN, 2.44-4.08) and PO4-P (5.40). N and P losses were dominated by sediment, and up to 95.70% of the total phosphorus and 66.08% of TN occurred in sediment. Nutrient loss exhibited the highest sensitivity to sediment yield compared to runoff and rainfall variables, and a significant positive linear relationship was observed between nutrient loss and sediment yield. SP contour ridge presented higher nutrient loss than that in PT contour ridge, especially for P loss. Findings gained in this study provide references for the response strategies of nutrient loss control to natural rainfall change in contour ridge system.