1. Water Quality Management Group, Dep. Soil and Environment; Swedish Univ. of Agricultural Sciences; PO Box 7014 SE-75007 Uppsala Sweden
2. Plant Nutrition and Soil Fertility Group, Dep. Soil and Environment; Swedish Univ. of Agricultural Sciences; PO Box 7014 SE-75007 Uppsala Sweden
3. Faculty of Agriculture and Life Sciences, PO Box 84; Lincoln Univ.; Lincoln 7647 Canterbury New Zealand