Evaluating and Improving Alternative Methods for Estimating Soil Erodibility and Water Erosion in Central Chile.

In the Revised Universal Soil Loss Equation RUSLE model, the soil erodibility factor K accounts for the influence of soil properties on soil loss during storm events in upland areas. The K-factor value is typically estimated using relationships based on physical and chemical soil properties. The objective of this study was to evaluate two of the most widely known methods for computing the K-factor values, and improve the RUSLE model estimates for soils in Central Chile. The first relationship, developed by Wischmeier and Smith (1978), uses soil texture and physical and chemical soil properties, and applies to soils with < 4% organic matter content. The second relationship, developed by Römkens et al. (1997), uses the soil particle size distribution. The RUSLE and the Römkens’ equation were used for computing the soil loss in 56 soil series from Central Chile, and compared with the estimates obtained with the Water Erosion Prediction Project WEPP model for the same soils. The results showed that RUSLE and WEPP provided similar average annual soil loss estimates, although the RUSLE estimates were typically higher than the WEPP predictions. For soils with < 4% organic matter, the K-factor values were also computed with the Wischmeier’s relationship and used to estimate the soil loss with RUSLE. The erodibility values obtained with this method were higher than the values computed with the Römkens’ equation, and even higher than the WEPP estimates. Finally, in order to improve the RUSLE estimates, both erodibility equations were calibrated using the entire set of soils from the study area. The improvement obtained in the RUSLE estimates demonstrated the convenience of calibrating these methods in order to get more reliable estimates when modeling water erosion.