1. Dep. of Soil and Environment; Swedish Univ. of Agricultural Sciences; Box 7014 750 07 Uppsala Sweden
2. National Soil Resources Institute, Cranfield Univ.; Cranfield Bedfordshire MK43 0AL UK
3. Institute of Landscape Ecology and Resources Management, Univ. of Giessen; Heinrich-Buff-Ring 26-32 35392 Giessen Germany
4. Bureau de Recherches Géologiques et Minières; Avenue C. Guillemin, BP6009 45060 Orléans, Cedex 2 France