Tillage erosion: An overview

Soil redistribution by tillage is becoming a recognized soil erosion process. Landscapes subject to tillage erosion are topographically complex or have a high number-of field boundaries. Tillage erosion contributes to the evolution of landscape heterogeneity through creation of distinct landforms and the relatively rapid redistribution of soils from upland positions to depressions. The resultant variability in soil properties has an important effect on crop production. Our objective is to provide a basic understanding of tillage erosion by describing the tillage erosion process and to discuss the effect of tillage erosion on soil properties, and soil productivity, and interaction with water erosion. A brief discussion is included on the subject of future research needs. A soil transport coefficient (k). has been determined as k = -Drhobbeta; where D is tillage depth (m), rhob is the soil bulk density (kg m(-3)), and beta is the slope of the linear regression equation of the relationship between soil displacement and slope gradient. This k-value effectively describes soil transport as a function of slope gradient for a variety of tillage operations; however, the gain or loss in soil mass at any point on the landscape is proportional to hillslope curvature. That is, soil loss from tillage operation will take place on convexities and upper field boundaries, while soil deposition occurs on concavities and lower field boundaries. Soil loss from tillage operations can commonly be greater than what is considered sustainable. As soil is,removed from upslope field boundaries or convex slope positions, subsurface soil horizons become exposed. The exposure and subsequent dispersion of this subsoil material, in addition to soil accumulation at lower slope positions, alters soil properties and introduces greater variation in soil properties over the landscape. The recognition of soil translocation by tillage and its subsequent effect on soil properties and variability presents considerable challenges. Soil conservation strategies must be broadened to include tillage erosion to be fully effective.