Soil surface roughness decay under different topographic conditions

Abstract

Soil surface roughness (RR) is one of the most significant factors influencing hydrological and erosion processes. It is most likely affected by topographic conditions, but this relationship has not been quantified. This study was conducted to detect the effects of topographic conditions on soil surface roughness decay after tillage and to determine the dominant mechanism affecting RR on the Loess Plateau. From June 10 to October 3, 2017, RR was measured using a handheld 3D scanner in six plots with different slope gradients and at three different slope positions along a 60 m plot. The results showed that soil surface roughness was significantly affected by slope gradient and position. RR increased exponentially with an increase in slope gradient (R2 = 0.97). The middle slope position exhibited the maximum RR, whereas the downslope position exhibited the minimum RR. Soil surface roughness decreased exponentially over time after tillage under different topographic conditions ranging from 0.91 to 4.50 mm. For the six plots with different slope gradients, rapid decreases in RR occurred from July 24 to Sept. 10, but for the three different slope positions, rapid decreases occurred from June 10 to July 24. RR declined exponentially with an increase in cumulative rainfall (266.4 mm, R2 = 0.88) and kinetic energy (38.9 MJ ha−1, R2 = 0.92). Cumulative kinetic energy was a better predictor of RR decay than cumulative rainfall at different slope positions. However, for plots with different slope gradients, RR decay after tillage was best estimated by slope gradient and cumulative rainfall (NSE = 0.95) or kinetic energy (NSE = 0.96). After tillage, the soil bulk density, crust thickness and soil cohesion increased significantly over time under different topographic conditions. RR decreased linearly with increasing bulk density, crust thickness, and cohesion. The breakdown of aggregates or clods was the dominant process leading to soil surface roughness decay in this study.