Clod movement and tillage tool characteristics for modeling tillage erosion
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abstract
Soil erosion caused by tillage is proportional to the local slope curvature. The value of the coefficient of proportionality (tillage transport coefficient) depends on the interaction between tillage tool and soil. These interactions have been modeled as a three-phase motion: drag (depending only on tool characteristics), when the soil is in contact with the instrument; jump (not necessarily present for all tools), when the soil loses contact with the tool and is ejected; and rolling, when the clods roll and jump in relatively close contact with the soil surface. Three sets of equations have been proposed and assembled into a computer program (SETi, from Soil Erosion by Tillage). The model simulates the 3D behavior of the transported soil. The performance of SETi is illustrated for the case of the moldboard plow. The simulated trends closely resemble those observed in experimental studies of tillage translocation. The major improvement with respect to previous models is that tool characteristics are explicitly taken into account. Tillage erosion is one of the major soil redistributing processes within the field border. Recent research has shown that that tillage erosion is often proportional to the local slope curvature (i.e., the rate at which slope gradient varies per unit of length). In present-day models, the proportionality coefficient is considered to be a black-box coefficient, depending on tillage tool and soil characteristics. To make the relationship between tillage translocation, soil, and tool characteristics more explicit the process of soil translocation must be better understood. We have found that there are three phases of motion, each described by its own set of equations, namely, drag, jump and rolling. Each phase depends on measurable characteristics of the tillage tools and of the soil. These equations have been implemented in the SETi computer model. At present, the model has been parameterized for a moldboard plow. The simulated soil transport reproduces the trends shown in the literature, indicating that the model behaves realistically. In its present form it can already be used for calculating the tillage transport coefficient needed by the existing tillage erosion models, as well as for designing less erosive tillage tools.
