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

Abstract

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 20m) and rainfall intensities (75, 50 and 25mmh−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.