Empirical modeling of soil erosion using unit plot data at Sparacia experimental area (southern Italy)

Purpose: Soil loss estimation by the Universal Soil Loss Equation (USLE) - based approach is widely used to perform soil conservation interventions. The recently proposed USLE-MB model explicitly accounts for plot runoff coefficient in the erosivity factor. Both the USLE and the USLE-MB can be deduced using a reference condition given by the unit plot, which is characterized by fixed length, steepness and bare soil tilled along the steepest slope. There is little evidence about the existence of the unit plot among those used to develop the USLE model, and few investigations experimentally considered this condition later. Methods: In the present investigation, the USLE and USLE-MB models were parameterized using measurements performed in the Sparacia unit plots, in Sicily. Results: The USLE soil erodibility factor differed significantly from the nomograph value and also from the estimates previously obtained by two methods applied to measurements collected in plots having different length and steepness compared to the unit plot. The experimentally determined soil erodibility factor of the USLE-MB also differed from those determined with these two methods. The slope steepness factor determined according to its definition was not consistent with that estimated with known literature relationships. The slope length factor was nearly constant for the USLE and assumed to be constant for the USLE-MB, in contrast with the increasing relationship with the plot length suggested by the USLE. Conclusion: This investigation elucidated the discrepancy between the single factors of the models obtained using measurements from the unit plot and those otherwise estimated.