Quantifying sheet erosion in agricultural highlands of Sri Lanka by tracking grain-size distributions

The reduction of productivity in arable lands of the tropical highlands through intensified soil erosion is a major reason for food scarcity in many developing countries. Identifying soil erosion hot spots in highland agricultural croplands and monitoring the effectiveness of soil conservation are crucial for improving land management practices. This paper develops a low cost and efficient method to quantify the rate of soil loss caused by splash and sheet erosion, in-situ at the plot scale. This method assumes that textural differences between the topsoil and the underlying soil within the plot are due to erosion of the top layer. Grain size analyses conducted in agricultural soils of the Upper Uma Oya Catchment (UUOC) of Sri Lanka provided data to quantify splash or sheet erosion and deposition. Net soil loss from the plot was calculated based on rates of area weighted soil loss and deposition. The net splash and sheet erosion rate in the plot was 20 t ha−1 yr−1, which is comparable with previous soil erosion results obtained in the area (25 t ha−1 yr−1) at similar temporal and spatial scale and under the same agricultural use. This study suggests that approximately half of the total erosion in the UUOC area results from splash and sheet erosion, whereas the rest is driven by concentrated flow through rill and gully erosion. This method is potentially transferable to other croplands as a robust approach for rapid measurement of splash and sheet erosion.