1. KULeuven; Earth and Environmental Sciences; Celestijnenlaan 200 3000 Leuven Belgium
2. Universität Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics; 70593 Stuttgart Germany
3. Kasetsart Univ.; Dep. of Soil Science
4. Forschungszentrum Jülich; Agrosphere (IBG-3) 52425 Jülich Germany