Soil tillage is usually considered as a process having only an indirect 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 redistribution by tillage can be described by a diffusion-type equation, which allows the intensity of the process to be characterized by a single number, which may be called the diffusion constant. The experimentally determined values of the diffusion constant vary between 100 and 400 kg mpl apl. This implies that erosion and sedimentation rates 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 results corroborates this conclusion. Therefore, tillage should be considered as a soil degradation process per se, rather than a process which makes the soil more sensitive to erosion.

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Off-site impacts of soil erosion are of greater social and economic concern in Western Europe than on-site impacts. They fall into two related categories: muddy flooding of properties and ecological impacts on watercourses because of excessive sedimentation and associated pollutants. Critical to these impacts is the connectedness of the runoff and sediment system between agricultural fields and the river system. We argue that well-connected systems causing off-site damage are not necessarily related to areas of high erosion rates; emphasis should therefore be on the way in which connections occur. In temperate, arable systems, important elements of connectivity are anthropogenic in origin: roads, tracks, sunken lanes, field drains, ditches, culverts and permeable field boundaries. Mapping these features allows us to understand how they affect runoff and modify its impacts, to design appropriate mitigation measures and to better validate model predictions. Published maps (digital and paper) do not, by themselves, give sufficient information. Field mapping and observation, aided by remote sensing, are also necessary. K E Y W O R D Sconnectivity, field mapping, off-site impacts, runoff and sediment flux, soil erosion

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