Rill and interrill erodibility and sediment characteristics of clayey Australian Vertosols and a Ferrosol

For soils and conditions outside the USA, input parameters for physically based soil erosion models, such as the WEPP model, are usually not available, particularly for tropical soils. In a laboratory study, small erosion pans and a programmable rain simulator were used to determine interrill erodibility, whereas in the field, rills were physically allocated in the field as plots of 0.1 by 10 m within a ridge–furrow arrangement and five water-inflow rates were applied sequentially to determine rill erodibility and critical hydraulic shear. During the rain or inflows, runoff samples were taken and flow was characterised. The soils tested were Grey Vertosol, Black Vertosol, and Red Ferrosol. The fall velocity parameter, V50, for rill soil and eroded sediment followed the order Red Ferrosol > Grey Vertosol > Black Vertosol, which Black Vertosol was the same order as observed for V50 and mean weight diameter (MWD) of aggregates in the interrill erosion experiment and D50 of interrill eroded sediment, demonstrating differences between soils in dispersion and aggregate stability. The estimated values obtained by the WEPP model were not comparable to laboratory interrill erodibility values or to field rill erodibility values. Thus, erodibility parameters for physically based erosion models such a WEPP should be determined in the field for tropical soils, and new equations need to be developed to estimate such values based on soil properties for tropical soils.