Runoff and losses by erosion in soils amended with sewage sludge

In order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha(-1) of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally-dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13.8 t ha(-1) of composted sludge, 50 t ha(-1) of fresh sludge and 11.3 t ha(-1) of thermally-dried sludge. The surface addition of a single application of thermally-dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally-dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally-dried sludge is the most efficient way to enhance soil infiltration. Copyright (C) 2003 John Wiley Sons, Ltd.