The effect of tillage direction on soil redistribution by mouldboard ploughing on complex slopes

Seven mouldboard ploughing experiments were conducted to systematically investigate the effect of different tillage directions on soil redistribution on hillslopes. The present study included tillage directions other than parallel to the gradient or along the contour, that is, in our experiments the slope gradient changed simultaneously in tillage and in turning direction. Using physical tracers we developed a model of the two-dimensional tracer displacement as a function of topography and tillage variables. The displacements in tillage and in turning direction were separately described as 2nd degree polynomials in both tillage and in turning directions. This model fully accounted for the directionality of tillage. Displacement in turning direction additionally depended on tillage depth, while that in tillage direction was affected by tillage speed and soil bulk density. We found a large effect of tillage directionality on soil redistribution, and tillage at 45° to the gradient turning soil upslope was the least erosive tillage direction. We obtained non-linear relationships between soil redistribution and profile curvature, instead of the linear relationships reported previously. Consequently tillage erosivity varied in tillage direction and a unique tillage transport coefficient could not be obtained for all tillage directions.