Use and misuse of the K factor equation in soil erosion modeling: An alternative equation for determining USLE nomograph soil erodibility values

•Improve/specify K factor equation used in many erosion models•Transfer original K factor nomograph into a set of equations•Quantify potential error of commonly applied K factor equation using 20,000 soils

The K factor of the Universal Soil Loss Equation is the most important measure of soil erodibility that was adopted in many erosion models. The K factor can be estimated from simple soil properties by a nomograph. Later, the classical K factor equation was published to assist the calculation of K. This equation, however, does not fully agree with the nomograph, which still has to be used in these deviating cases. Here we show for a large soil data set from Central Europe (approximately 20,000 soil analyses) that the equation fails in considerably more than 50% of all cases. The failure can be large and may amount to half of the K factor. To facilitate the K factor calculation, we developed a set of equations that fully emulates the nomograph and supersedes the cumbersome reading of the nomograph.