Comment on “Determining soil erodibility for the USLE-MM rainfall erosion model by P.I.A. Kinnell”

The measurements units of the USLE-MM soil erodibility factor are dependent on the exponent of the erosivity term. This circumstance prevents to compare soil erodibility values of sites differing by the value of this exponent. To overcame this problem, Kinnell (2018) suggested to relate the soil erodibility factor of the USLE-MM with that of USLE-M by a linear relationship with the objective to obtain a soil erodibility factor independent of the power of the erosivity term. The USLE-MB, which is a recently proposed model, has also a soil erodibility factor having measurement units common to USLE modelling environment. Kinnell (2018) also showed that the relationship between the power of erosivity term and the coefficient of proportionality of the linear relationship between soil erodibility of USLE-MM and USLE-M is site independent. In this comment, using the database of Sparacia experimental area, both this geographical independence and the linearity hypothesis between soil erodibilities were tested. The linearity hypothesis was not completely consistent for Sparacia experimental area while it was more satisfied for the comparison between soil erodibility of USLE-MB and USLE-M. The exponential equation proposed by Kinnell (2018) between the power of erosivity term and the coefficient of proportionality was demonstrated to be site-dependent.