Runoff and soil loss as influenced by selected stability parameters and cropping and tillage practices

Abstract

Water-stability of surface soil aggregates is probably the most important property governing soil detachment by rain impact. The relative importance of water-stability parameters [i.e. wet aggregate stability (WAS), tensile strength, dispersible clay (DC)], for predicting runoff and soil loss has not been resolved. The objectives of this study were to compare (i) the influence of WAS, DC, and time to ponding (TP), and (ii) cropping and tillage practices on rain-induced runoff and soil loss. A cropping and tillage system experiment with four replications was established on a silt loam soil in 1988 in Ontario, Canada. The cropping treatments were conventionally cultivated corn, different forages following conventional corn, and conventional corn following forages grown for different lengths of time. The tillage treatments were: conventional- and minimum-till. Using a portable rainfall simulator 96 rainfall simulations were carried out during the 1991 and 1992 growing seasons. The influence of cropping and tillage treatments on runoff, sediment loss, WAS, DC, TP and surface cover (SC) was significant at P < 0.05 for the data pooled for both growing seasons. Multiple regression analysis indicated that a reduction in DC from 3 to 2%, induced by forages in rotations, resulted in 15% reduction in runoff and 11% for soil loss. A similar analysis for TP indicated that an increase in WAS or SC from 25 to 30%, induced by forages or minimum-till practice, resulted in 27% increase in TP for WAS and 15% for SC. Even though soil loss was not directly influenced by WAS, the latter had an impact on soil loss through TP. Thus, in the absence of data on TP, information on both WAS and DC would be required to predict soil loss during rain events.