Estimation of erodibility factor (K) using the RUSLE model in some soils of the semi-arid regions in northwest of Iran

Soil loss is commonly predicted using the revised universal soil loss equation (RUSLE) worldwide. Soil erodibility (K) is one of factors affecting soil loss essential to predict water erosion. In this study, soil loss was measured under 41 natural rainfall events at standard plots located in 36 different fallow lands with 9% slope in Hashtroud, a semi-arid region in the northwestern of Iran from March 2005 to March 2007. Soil erodibility factor (K) values were measured based on the soil loss per unit of rainfall-runoff erosivity factor (R) and also estimated on the basis of geometric mean diameter of soil particles (Dg) for 36 lands. Estimated K value (0.038703 t h MJ-1 mm-1) was on average 50.98 times higher than the measured value (0.000483 t h MJ-1 mm-1) in 36 lands. Regression analysis indicated that the measured K is significantly (P<0.001, R2=90) related to the aggregate stability and soil permeability. Relationship between the measured K value and easily-measurable soil properties (mineral particles, gravel, organic matter, lime and potassium) was analyzed. Results showed that the measured K value is significantly (P<0.001, R2=0.82) influenced by Dg, organic matted and lime. This study revealed that the aggregate stability and soil permeability are the two important dependent soil properties affecting soil erodibility (K), affected by mineral particles, organic matter and lime. Soil properties that increase the aggregate stability and permeability can decline the soil erodibility. Lime is one of the soil properties that has an important role in declining the soil erodibility in soils of the semi-arid regions.