1. Institute of Agricultural Sciences; ETH Zurich; Eschikon 33 CH-8315 Lindau Switzerland
2. Institute of Crop Science and Resource Conservation (INRES); Soil Science and Soil Ecology; Nussallee 13 D-53115 Bonn Germany
3. Forschungszentrum Jülich GmbH; Agrosphere Institute (IBG-3); Wilhelm-Jonen-Str. D-52425 Jülich Germany
4. Geological Institute; ETH Zurich; Sonnegstrasse 5 CH-8092 Zurich Switzerland