SOIL DETACHMENT BY SINGLE RAINDROPS OF VARYING KINETIC-ENERGY

Soil detachment by raindrop impact initiates surface seal formation and interrill erosion processes. Experiments were conducted to study the effect of soil strength on soil detachability (K(d)) and threshold kinetic energy (KE(o)) parameters of the single-drop detachment model D = K(d)[KE - KE(o)], where D is soil detachment from raindrop impact and KE is raindrop kinetic energy. Soil detachment by single raindrops with varying kinetic energy was measured on samples taken from Ap horizons of seven soils ranging in texture from loamy sand to clay. Different soil-strength conditions were simulated by varying bulk density and soil matric potential. Soil strength was characterized by fall-cone measurements. Both K(d) and threshold kinetic energy needed to initiate soil detachment, KE(o), depended on soil strength and clay content. In sandy and loam soils with low strength conditions, KE(o) was about 0.1 mJ; with higher strength conditions, KE(o) varied from 0.2 to 0.3 mJ. For clay soils with different strength conditions, KE(o) ranged from about 0.2 to 0.6 mJ. The relationships of K(d) and KE(o) with soil strength for the seven soils were grouped into three broad textural groups of sands, loams, and clays. Within each group, the K(d) decreased and the KE(o) increased with increase in soil strength.