Between Year Variation in Soil Erodibility Determined by Rainfall Simulation

RAINFALL simulation has been used since the 1960's to determine how soil erodibility is related to basic soil physical and chemical properties. Erodibility values determined in this manner have been assumed to be time invariant. The objective of our research was to test the hypothesis that soil erodibility values determined from rainfall simulation on bare, recently tilled soils do not change from year to year. We used standard rainfall simulation equipment to test two fertile, agricultural soils in two successive years. The soils occurred on the same landscape in close proximity to one another and had the same management history. Soil tillage and plot preparation practices were identical between years. Variables evaluated included total runoff and soil losses, equilibrium runoff and soil loss rates, USLE K factors, interrill erodibility (Kj) values, and rill erodibility (K^) values. The variation between years was highly significant (p<0.01) for many of the variables evaluated. The variation in soil loss between soils was much greater than the variation in runoff. There was a significant (p<0.05) interaction between year and soil for many of the variables evaluated. The interaction occurred because one soil showed similar behavior between years, while response from the other soil was considerably different.