Wisconsin Buffer Initiative
Universal Soil Loss Equation
The revised universal soil loss equation (RUSLE) is an equation that predicts soil erosion loss due to rainfall and runoff. The equation was developed through funding from the United States Department of Agriculture in an effort to reduce soil loss through conservation planning practices. RUSLE is an updated version of the original Universal Soil Loss Equation (USLE), published in Agriculture Handbook No. 537 (described in handbooks by Wischmeier and Smith 1965, 1978). The calculations in RUSLE are more involved than USLE and are facilitated with computer programs. The equation takes into consideration several different variables to come up with soil loss per year in tons per acre. The variables considered are as follows:
- A = estimated annual average soil loss, expressed in the units selected for K and for the period selected for R (ton acre -1 year -1 ).
- R = rainfall runoff erosivity factor, quantifies the effects of raindrop impact while also taking into account any significant effects from rainfall and snowmelt runoff.
- K = soil erodibility factor, the ease with which the soil is lost from raindrop impact, rainfall runoff, or both. Represents the effects of soil properties and soil profile characteristics on soil loss.
- L = slope length factor, the ratio of soil loss from the field slope. Horizontal distance form the origin of flow to where either: deposition starts to occur or runoff becomes concentrated and forms a channel.
- S = slope steepness factor, the ratio of soil loss from the area of interest to soil loss from a standard field slope under otherwise identical conditions.
- P = support practice factor, the ratio of soil loss with a support practice like contouring, stripcropping, terracing to soil loss with straight-row farming up and down the slope.
By using geographic information system (GIS) and inputting data layers for each of the above variables we are able to predict where, in each of the WBI's watersheds, buffers are needed the most. Eventually we will have an interactive map whereby the user, farmers or otherwise, can input a value for the support practice factor, and generate their own numbers for average annual soil loss in tons-per acre-per year.
