Simulating long-term soil redistribution generated by different patterns of mouldboard ploughing in landscapes of complex topography

In agricultural landscapes, translocation and redistribution of soil during tillage operations have been described as intense geomorphic, soil degradation and erosion (mechanical or tillage erosion) processes. This paper presents the design and calculation algorithms of the Soil Redistribution by Tillage (SORET) model. The SORET model is of the spatial distribution type and can perform 3D simulations of soil redistribution in Digital Terrain Models (DTMs) on the field scale. It can predict soil redistribution arising from different patterns of tillage in a given landscape via computer simulation of a single tillage operation, and is also able to forecast the long-term effects of repeated operations. Using the model, simulation was made of the long-term effects of three different patterns of tillage achieved using a mouldboard plough: (i) contouring, (ii) up–downslope, and (iii) downslope alone. The DTM selected was a field of complex topography and up to 40% slope with a Calcic Haploxeralf (Calcic Luvisol) soil in Central Spain. Results indicate substantial differences in the effects of the three tillage patterns in terms of absolute soil erosionaccumulation rates and the spatial distribution of areas of soil loss and deposition. These findings also suggest complex interaction between topography and direction of tillage, which ultimately determines the intensity and pattern of soil redistribution. Repeated downslope tillage gave rise to most intense soil degradation by tillage erosion, with an eroded area of 62% of the DTM, and an average erosion rate of 27.8 Mg ha(-1) per tillage operation. For contouring tillage, the eroded area was 59% of the total DTM and the average erosion rate was 16.7 Mg ha(-1) per tillage operation; for up–downslope tillage, these variables were 67% and 15.1 Mg ha(-1), respectively. The SORET model appears to be a useful tool for simulating the spatial variability of soil redistribution and soil erosion-accumulation rates determined by different patterns of tillage in the long term. However, additional field data on the initial variability of soil properties are required if the effects of soil redistribution on soil degradation are to be adequately evaluated.