Drying, soil surface condition and interrill erosion on two Ontario soils

Interrill erodibility summarizes the resistance of soil to rainsplash, sheetwash and rainflow erosion and incorporates changes in infiltration, roughness and resistance to detachment and transportation. Resistance to interrill erosion varies during storms, reflecting the effect of wetting, sealing, crusting, and erosion on surface conditions. Significant changes in soil conditions also occur as a result of progressive drying between storms, producing considerable uncertainty in event-based erosion prediction. However, a clear link between drying, primary soil properties and soil condition, as well as interrill erosion during subsequent storms has not been established. In this study, soil condition and interrill erosion of soils from southern Ontario were examined in detail during a sequence of simulated rainstorms, and linkages between primary soil properties, drying, surface soil structure, and interrill erosion were established. Interrill erosion after drying differed depending on the persistence of the changes in soil structure caused by drying. Pronounced stabilization of aggregates on drying led to an increase of erodibility, indicating a transition from a coherent to granular structure, requiring lower stresses for particle detachment. The sensitivity of soil erodibility to drying appears to be determined by the tendency of a soil to form aggregates. The results show that a better understanding of the linkages between primary soil properties, rainfall and drying history, soil condition and interrill erosion is required for effective event-based erodibility assessment. However, the wide range of possible initial soil conditions and the complex nature of soil–climate interaction are likely to limit the effectiveness of erodibility assessment.