THE RELATIVE CONTRIBUTION OF SOIL TILLAGE AND OVERLAND FLOW EROSION TO SOIL REDISTRIBUTION ON AGRICULTURAL LAND

This study uses evidence for the long-term (35 years) pattern of soil redistribution within two agricultural fields in the UK to identify the relative importance of tillage and overland flow erosion. Spatially distributed long-term total soil redistribution data for the fields (Dalicott Farm and Rufford Forest Farm) were obtained using the caesium-137 (¹³⁷Cs) technique. These data were compared with predicted patterns of soil redistribution. Recent studies have demonstrated that the redistribution of soil by tillage may be described as a diffusive process. A two-component model was, therefore, developed which accounts for soil redistribution by both overland flow and diffusive processes. Comparison of the predicted patterns of overland flow erosion alone with the observed (¹³⁷Cs-derived) data indicated a poor agreement (r² = 0.17 and 0.11). In contrast, a good agreement exists between the predicted pattern of diffusive redistribution and the observed data (r² = 0.43 and 0.41). These results give a clear indication that diffusive processes are dominant in soil redistribution within these fields. Possible diffusive processes include splash erosion, soil creep and tillage. However, the magnitude of the diffusion coefficients for the optimum predicted pattern (c. 350–400 kg m^?1 a^?1) demonstrates that tillage is the only process capable of explaining the very significant soil redistribution which is indicated by the ¹³⁷Cs data. Consideration is given to the implications of these results for both soil erosion prediction and landscape interpretation.