1. Research Group of Soil Fertility and Nutrient Management; Department of Soil Management; Ghent University; Coupure Links 653 9000 Gent Belgium
2. Institute of Soil, Water and Environmental Sciences; The Volcani Center, Agricultural Research Organization; POB 6, 50250 Bet Dagan Israel
3. Department of Environment and Planning; Centre for Environmental and Marine Studies, University of Aveiro; 3810-193 Aveiro Portugal