THE ROLE OF TILLAGE IN SOIL REDISTRIBUTION ON HILLSLOPES

Soil tillage is usually considered as a process having only an indirec t influence on soil erosion. This paper describes the results of field experiments carried out with a mouldboard and a chisel plough showing that an important net downslope soil movement can be associated with soil tillage. Available experimental evidence suggests that the soil r edistribution by tillage can be described by a diffusion-type equation , which allows the intensity of the process to be characterized by a s ingle number, which may be called the diffusion constant. The experime ntally determined values of the diffusion constant vary between 100 an d 400 kg m(-1) a(-1). This implies that erosion and sedimentation rate s associated with tillage may be more important than those associated with water erosion on much of the hilly arable land in western Europe. A comparison of recent hillslope evolution with model simulation resu lts corroborates this conclusion Therefore, tillage should be consider ed as a soil degradation process per se, rather than a process which m akes the soil more sensitive to erosion.