Soil Dispersibility, Rain Properties, and Slope Interaction in Rill Formation and Erosion

Abstract

AbstractSoil erosion increases with slope steepness. We hypothesized that the rate at which short‐slope soil erosion increases with slope steepness depends on the prevailing erosion mechanism, which in turn depends on soil dispersibility and rain properties (impact energy of drops and water quality). Soil dispersion, as a function of exchangeable sodium percentage (ESP) and water quality, was determined by shaking soil samples in deionized water (DW) or tap water (TW). Clay dispersion increased with increases in soil ESP and was prevented by the electrolyte concentration in TW. We studied the effect of soil ESP, water quality, and the impact energy of rain on soil erosion while maintaining similar runoff. To do so, we first exposed the soil samples to DW rain on a 5% slope until a surface seal developed. Then we increased the slope to 35% and changed the water quality and impact energy of the rain. Runoff volumes were unaffected by rain properties at the 35% slope. Soil losses increased with increases in the ESP of the soil. Soil losses varied with rain properties in the following order: DW rain > TW rain = DW rain with low energy (mist) > TW mist. Rills were formed by both DW rains (high impact energy and mist). The extent of rilling increased with soil ESP. No rills were formed by TW rains. Under dispersive conditions (sodic soils and DW), runoff was sufficient to initiate rilling and soil losses increased sharply with slope.