RILL EROSION DEPENDENCE ON SOIL-WATER CONTENT, AGING, AND TEMPERATURE

Soil shear strength and cohesion at high water content and low bulk de nsity determine rill erosion. Aging of wet soil samples at different t emperatures may increase the cohesion forces between soil particles. T he effects of soil water content (100-500 g kg(-1)), aging (15 min, 4 and 24 h) and temperature (25, 40, and 60 degrees C) on rill erosion o f three soils, a grumusol (Typic Chromoxerert), a loess (Calcic Haplox eralf), and a hamra (Typic Rhodoxeralf), were studied in the laborator y using a small hydraulic flume. For water contents above air dried, r ill erodibility (RE) decreased with increased aging. Optimum water con tents for development of cohesion differed for the grumusol and loess. The effect of aging on RE depended on soil type. At no aging, RE was the highest in the clay grumusol (3.26 x 10(-3) s m(-1)) and the lowes t in the loamy sand (0.52 x 10(-3) s m(-1)). With increased aging to 4 and 24 h, RE of the grumusol decreased to 0.24 x 10(-3) s m(-1) but t he RE of the hamra was not affected. Development of biological and che mical cohesion forces determine RE changes with aging. At 60 degrees C the biological mechanism diminished and the chemical mechanism predom inated. High water content and high temperature (high Brownian motion) during aging enhance clay-to-flay contacts and cementation of soil pa rticles into a cohesive structure that resists rill erosion.