Understanding the combined effect of soil properties on gully erosion using quantile regression

Abstract

The individual effects of soil properties on soil erodibility are well understood. It is also known that various interactions between these properties exist, which creates the need for unique investigations into how soil properties influence soil stability. Quantile regression was used in this paper to determine which soil properties control gully erosion in a catchment in Lesotho. Samples of typical soil forms found in the catchment were analysed for properties related to soil erosion. Dispersion ratio had the best correlation with areas of severe gully erosion. No strong correlation was found for a single soil property with dispersion ratio. Quantile regression showed that a combination of effective cation exchange capacity (CEC), total carbon, exchangeable sodium percentage (ESP) and free iron influenced soil dispersion. When the aggregating agents (effective CEC, total carbon and free iron) are deficient in the soil sample, very small amounts of a dispersing agent (ESP > 0.67%) will lead to above-average dispersion. Soils with an increased amount of basaltic parent material tended to be more stable.

Keywords: aggregation, dispersion, exchangeable sodium percentage, piping

South African Journal of Plant and Soil 2014, 31(3): 163–172