1. Department of Environmental Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, SE-750 07 Uppsala, Sweden
2. Soil and Water Management Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Department of Soil, Water and Climate, Room 439, 1991 Upper Buford Circle, University of Minnesota, St. Paul, Minnesota 55108
3. Department of Soil Sciences, Swedish University of Agricultural Sciences, P.O. Box 7072, SE-750 07 Uppsala, Sweden