WEPP interrill erodibility for clay soils in the crop lands of Northern NSW and Southern Queensland, Australia

Abstract

Context Water Erosion Prediction Project (WEPP) soil erosion model parameters are rare for cultivated cropping soils in Australia. Aims Measure WEPP interrill erodibility (Ki) for cropping soils. Methods Plots were 50% side-slopes of row-crop furrows. Rainfall was applied for 30 min at 107 mm h−1 under a rainfall simulator, then at higher and lower rainfall intensities for 10 or 6 min. Several of these rainfall sequences were performed with drying between (events). Runoff, sediment concentrations and sediment sizes in runoff and the soil surface after rain and sediment settling velocities were measured. Soils were well-aggregated Vertosols and a Dermosol: clay 31–69%, silt ~20%. Settling velocities and undispersed particle size distributions for rainfall wet soil are provided for a range of soils in Supplemental Data, for use by WEPP users. Key results Runoff during 30 min and 54 mm of rain was 28–44 mm or 50–86% rainfall. Soil losses were 26–61 t ha−1 and sediment concentrations 67–127 g L−1. Infiltration, runoff, sediment concentration and soil losses were sometimes different for soils and events. Gatton and Emerald soils had lower soil losses and Cecilvale, Mywybilla and Narrabri soils had higher soil losses. Conclusions Mean Ki for Emerald and Gatton soils were significantly lower, 2 960 000 and 3 209 600 kg.s m−4, respectively. Ki values were not significantly different for the Cecilvale, Narrabri and Mywybilla soils, 3 900 000 kg.s m−4. Implications WEPP Ki values were like values found for USA cropping on clay soils. Sizes in the soil surface and sediment, and settling velocity distributions, were similar between soils but sediment sizes were finer.