1. Nutrient Management Institute, Nieuwe Kanaal 7C, 6709 PA Wageningen, Netherlands
2. Environmental System Analysis Group, Wageningen University and Research, P.O. Box 47, 6700AA Wageningen, the Netherlands
3. Environmental Research, Wageningen University and Research, P.O. Box 47, 6700AA Wageningen, the Netherlands
4. Plant Research, Wageningen University and Research, P.O. Box 16, 6700AA Wageningen, the Netherlands