Soil crust formation as affected by slope gradient on clay soils of semi-arid Machakos District, Kenya

Abstract

Surface crusts formed by impact of raindrop restrict water infiltration into soil. The decrease in infiltration not only leads to an mcrease in surface flow and accelerated erosion, but also to reduced available water to plants. Upon drying the surface crust may impede plant emergence and growth, thereby reducing yield. This study was carried out with the aim of assessing the effect of slope gradient on crust properties with a view of developing elationships between crust formation and slope gradient when soil is subjected to natural rainfall. A surface of the top horizon (Ap) of a chromic Luvisol was exposed to rainfall at four slope gradients (1 %, 10%,20% and 30%) for two rain seasons. Crust thickness, crust strength and crust conductance were measured under various cumulative rainfall amounts. Thick and strong crusts were observed at the soil surface after the first rainfall event. Crust thickness and strength were significantly different (PO .05) between slope gradients, with crust formation being more pronounced at lower slop gradients (1% and 10 %) compared to higheI slope gradients (20% and 30%). Both crust thickness and strength followed a similar trend; as cumulative rainfall increased, they showed a slight increase after 2-3 storms, followed by a gradual decline as rainfall increased. Crust conductance was reduced by between 60% and 80% after the first ramfall event, and increased thereafter as the surface crust continued to decay with rainfall increase. Crust conductance was more strongly correlated to crust thickness (r