The effect of tillage depth, tillage speed, and soil condition on chisel tillage erosivity

In this study, a series of tillage experiments were set up to investigate the effect of variations in tillage depth and tillage speed on net soil displacement and the associated tillage erosion rates for up and downslope chisel tillage of a loamy soil under two different soil conditions: 1.) a consolidated soil under stubble vegetation (primary pass), and 2.) a freshly tilled, loosened soil (secondary pass). The experimental results show that the average displacement distance is not only a function of slope gradient, but also of soil condition, tillage depth, and speed. A model incorporating these additional effects was proposed and validated using data available in the literature: variations in displacement distance can be successfully predicted, but their absolute magnitude is probably also controlled by tillage implement geometry, which is at present not incorporated into the model. The fact that displacement distances are not affected by slope gradient only complicates the calculation of tillage erosivity. However, if only the controlled variations in tillage depth and speed are accounted for, the use of a single tillage transport coefficient k is still possible without an unacceptable loss of accuracy. Using the model, a series of nomograms have been developed that allow one to evaluate the effect of tillage depth and/or speed on soil erosivity of a given tillage operation. These nomograms are a valuable tool for evaluating possible strategies to remediate tillage erosion due to chisel tillage. Finally, experiment results show that chisel tillage in the Belgian Loan Belt is very erosive, leading to annual erosion rates exceeding 2 mm yr(-1) (0.08 in yr(-1)) locally.