1. Group of Plant Nutrition, Inst. of Plant Sciences, Swiss Federal Institute of Technology (ETH Zürich)CH‐8315Eschikon‐LindauSwitzerland
2. Soil Science, INRARD 10 (Route de Saint Cyr)F‐78026VersaillesCedexFrance
3. Soil, Plant, and Ecological Sciences Div., P.O. Box 84Lincoln Univ.CanterburyNew Zealand