Hi! The best book I know for the USLE equation is the following: Brooks, K.N., Ffolliott, P.F., Gregersen, H.M., Thames, J.L. (1991) HYDROLOGY AND THE MANAGEMENT OF WATERSHEDS, Iowa State University Press/Ames. 392 p. ISBN: 0-8138-0137-0 For all the subjects related to watershed management, you can't miss that book! Gook luck, Michel Chevalier