1. Agrosphere, Institute of Bio- and Geosciences (IBG-3); Forschungszentrum Jülich GmbH; Jülich Germany
2. Earth and Life Institute, Univ. catholique de Louvain; Louvain-la-Neuve Belgium
3. Dep. of Land, Air, and Water Resources; Univ. of California; Davis CA 95616
4. Institute of Crop Science and Natural Resource Protection, Faculty of Agriculture, Univ. of Bonn; Bonn Germany