Influence of microtopography, ridge geometry and rainfall intensity on soil erosion induced by contouring failure

Abstract

Contour ridging is an effective soil conservation practice used throughout the world. Because of microtopographic relief on sloping land, rainwater concentrates in low areas along furrows where contouring failure can occur. To quantify the effects and interactions of factors that influence runoff and sediment yield induced by contouring failure, a total of 32 rainfall simulation experiments were conducted, with two microtopography indices (row grade, RG, and field slope, FS), two ridge geometry indices (ridge height, H, and ridge width, W), and two levels of rainfall intensity (RI) arranged in an L16(25) orthogonal array with two replications. The results showed that all of the factors considered except for row grade exerted significant influences on runoff and sediment yield (p=0.01). Rainfall intensity was the most important factor for runoff, with a contribution of 68.1%, followed by ridge height, field slope, and ridge width. Field slope and rainfall interacted negatively, with a contribution of 5.4%, resulting in increased runoff with increasing field slope at lower rainfall intensities, while the opposite effect was observed at higher rainfall intensities. The negative interaction of ridge height and width and the positive interaction of field slope and ridge height also had significant effects on runoff. For sediment yield, the most important factor (21.4%) was ridge height, which had a negative effect. Rainfall intensity had less effect on sediment yield than on runoff, while the row grade and its interaction with ridge width had greater influences. The optimal combinations of factors for control of runoff were determined to be RG1, FS1, H2, and W2 for lower rainfall intensity and RG1, FS2, H2, and W2 for higher rainfall intensity, and the optimal combinations of factors for sediment yield conservation were determined to be RG1, FS1, H1, and W2, where in all cases, the subscripts 1 and 2 denote lower and higher factor levels.