Water drop impact angle and soybean protein amendment effects on soil detachment

To improve soil erosion prediction technology, the mechanics of each erosion process must be understood sufficiently to predict soil loss on an event basis. The mechanics of the initial erosion process, soil detachment caused by falling raindrops, requires greater understanding to improve mechanics-based prediction. This laboratory study addressed the effect of soil shear strength and raindrop impact angle on soil detachment. Loess (fine-silty, mixed, superactive, mesic Typic Hapludoll) and glacial till (fine-loamy, mixed, superactive, mesic Aquic Hapludoll) A and C horizon soil materials were used. To vary soil shear strength, soybean protein material was added to each soil material at concentrations of 0.0, 0.5, and 1.0% by weight. Soil shear strength and soil detachment were measured on preformed soil cores. Soil detachment tests were performed at water drop impact angles of 90, 80, 70, and 60 degrees. Soil strength increased and detachment decreased with increasing soybean protein concentrations. Shear strength of the loess C horizon increased 0.61 to 1.85 Mg m(-2), while that of the till C horizon material increased 0.57 to 0.98 Mg m(-2) with addition of 1% soybean protein. A 1%-soybean protein addition reduced soil detachment 26% compared with unamended soil. Significant soil detachment interactions existed between waterdrop impact angle and the other variables. These interactions were due to different mechanical behavior of the soils and changing strength caused by soybean protein additions. Interactions observed are explained based on differences in the lateral jet for varying impact angles and for elastic vs. inelastic impacts.