IMPACT OF SOIL-EROSION ON PRODUCTION IN CROPPING SYSTEMS .2. SIMULATION OF PRODUCTION AND EROSION RISKS FOR A WHEAT CROPPING SYSTEM

Maintenance of productive soil base by minimizing soil erosion is vital to long-term crop production. In this study, a modelling approach is used to estimate effects of soil erosion on productivity for a wheat cropping system at three locations in northeast Australia, Emerald, Dalby and Gunnedah. Predictions of erosion, runoff and yield decline due to erosion for variations in initial soil depth, slope and fallow management strategy are presented. Rates of yield decline were highest at Emerald due to summer dominance of rainfall resulting in higher runoff during summer fallow periods. On average, soil depth decreased by 0.35 cm year-1 at Emerald, 0.25 cm year-1 at Dalby and 0.1 cm year-1 at Gunnedah for a 50% slope, 100 cm initial soil depth and a disc/chisel fallow management strategy. Rates of soil removal and subsequent yield decline were higher for shallower soils, steeper slopes and if management practices provided less stubble cover during the fallow. The productivity half-life concept shows that the productive life of the soil was less than 100 years for some soil depth, climate, slope and management combinations. For other combinations, significant yield decline was predicted after 100 years of cropping. The quantification of erosion-productivity relationships allows us to identify regions of higher risk, to estimate the utility of management options, and provide a basis for focusing research and development of management strategies to preserve long-term production.