INTERILL erosion associated with raindrop impacts on bare soil surfaces has been characterized by many studies of vertical rainfall. Wind driven rainfall is of higher, more erosive energy and approaches the soil surface from nonvertical angles. Tall crop residues on conservation-tillage fields have varied effects on shielding the soil surface from direct raindrop impacts dependent upon the angle and direction of rainfall. Quantifying the effects of residue height and trajectory of rainfall on the effective soil cover could improve residue management techniques and erosion predictions. Undisturbed wheat and grain sorghum stubbles were viewed at various angles and orientations to determine the effective soil cover approached by winddriven raindrops. Angle of approach from vertical changed soil cover in every case. Orientation relative to row direction increased soil cover only for the special case of rain direction coincident with row direction in sorghum stubble. Increasing stubble height did not increase soil cover for sorghum as much as it did for wheat. Soil cover contributions from standing stubble were in addition to the approximately 50% soil cover from recumbent residues. A simulation model predicted soil cover for an idealized bare soil condition. The model was more sensitive to stubble height than was the empirical data
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Morrison et al. (1985) studied this question.