Slope length effects on processes of total nitrogen loss under simulated rainfall

• Slope length effects on runoff, soil and total nitrogen losses are proposed.
• Horton infiltration model best describe runoff process with 5 slope lengths.
• Power function fit relationship between runoff and soil loss with 5 slope lengths.
• Relationships among runoff, sediment and total nitrogen losses are presented.
• Model of total nitrogen loss under 5 slope lengths is established on slope scale.

Slope length effects on the processes of soil erosion have been the focus of research on hillslope hydrology and sediment transport. A field experiment was conducted to investigate the effects of slope lengths (1, 5, 10, 15 and 20 m) and rainfall intensities (75, 50 and 25 mm h− 1) on runoff, soil and total nitrogen (TN) losses under simulated rainfall conditions. Kastanozem was selected in the experiment. Generally, runoff rates and runoff-associated TN loss rates decreased with slope length, whereas sediment and sediment-associated TN losses increased with slope length under three rainfall intensities. The relationship between runoff and time could be described by the Horton infiltration model, with a correlation coefficient R2 > 0.85. The function parameters of final infiltration rate (if) and coefficient (c) were closely related to slope length, suggesting that a model of runoff processes correlated to slope length was established. There was a significant positive power relationship between runoff and sediment yield rates (p < 0.01). Runoff-associated TN losses were mainly controlled by runoff rates, whereas sediment-associated TN losses were mainly controlled by sediment yield rates, and positive linear correlations best represented their relationships. Because sediment-associated TN losses dominated the total TN losses, sediment yield rates were positively correlated with the total TN losses. Increasing rainfall intensity generally increased runoff, sediment yield and TN loss rates, but changes in rainfall intensity did not influence their relationships. This study demonstrated that a model could be established to simulate the processes of TN loss for different slope lengths.