1. Department of Soil Quality; Wageningen University; PO Box 47, 6700 AA Wageningen The Netherlands
2. Alterra; Wageningen University and Research Centre; PO Box 47, 6700 AA Wageningen The Netherlands
3. Department of Soil and Water Conservation and Waste Management; CEBAS; CSIC, PO Box 164, 30100 Espinardo, Murcia; Spain