Modelling the impact of erosion on soil productivity: A comparative evaluation of approaches on data from southern Brazi

Erosion changes soil properties, removes nutrients and alters crop yields. A knowledge of these impacts on soil productivity is needed for economic analyses of erosion and conservation. Based on a United Nations Food and Agriculture Organization experimental design to monitor these changes, results are reported from four research sites in southern Brazil on Ferralsols and Cambisols, enabling the construction of erosion-yield-time and nutrient loss relationships. Plot experiments ran for up to seven years of natural erosion, followed by one or two years of maize cropping. A remarkably consistent composite erosion-yield relationship in logarithmic form was found, showing a sharp yield decline with initial soil loss. Soil 'resilience' was identified through erosion-time relationships, 'sensitivity' through erosion-yield equations. As erosion progressed, losses of nutrients, especially of organic carbon and calcium, were significant. In situ, changes in soil properties were far less marked. Together with measured yield reductions caused by cumulative erosion, these results enabled the modelling of changes in soil productivity over time with respect to both soil quality and impact on yields. A production 'half-life' of between one and 39 years according to soil type and level of erosion was also identified.