1. Coltan Environmental Management, Central Africa P.O. Box 4415 Kigali Rwanda
2. University of Parakou Faculty of Agronomy P.O. Box 123 Parakou Benin
3. Universität Kassel Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics (OPATS) Steinstr. 13 37213 Witzenhausen Germany
4. University of Rwanda College of Agriculture Rwanda
5. Technische Universität Braunschweig Institute of Geoecology Braunschweig Germany