1. Savanna Agricultural Research Inst. (SARI), CSIR; P.O. Box 52 Tamale Ghana
2. Dep. of Geography; Seoul National Univ.; Shilim-Dong, Kwanak-Gu Seoul Korea
3. Center for Development Research (ZEF); Univ. of Bonn; Walter-Flex-Str. 3 53113 Bonn Germany