A soil and terrain digital database (SOTER) for improved land use planning in Central Benin

The soil is a natural resource, non-renewable in the short term and expensive either to reclaim or to improve following erosion or degradation. In the Republic of Benin (West Africa) the increasing pressure on land caused by steady population growth induces soil degradation. The reduced site productivity calls for an information system on soil resources, which allows the analysis of land suitability, potential food production, environmental impact of land use and the identification of conservation measures. On the basis of such a system, sound policy formulation and development planning at all levels can be carried out, utilizing both internal and external resources efficiently. For the central part of Benin, the development of a soil information system has been initiated. The data structure for the description of the land resources was established according to the Soil and Terrain Digital Database (SOTER) manual (Global and National Soils and Terrain Digital Databases (SOTER). Procedures Manual. International Soil Reference and Information Centre, Wageningen, The Netherlands, 1993) with slight modifications (Mitteilg. Dtsch. Bodenkdl. Ges. 76 (1995) 1221). Based on field observations and data analysis, land areas have been delineated showing similar response to management practices. On the uppermost level, seven so called 'terrain units' could be distinguished. The main differentiating criteria were landscape morphology, geology and hydromorphy. The terrain units are subdivided at a second level into 25 terrain components according to the soil parent material and landform. The FAO/ITC land suitability procedure was used to identify crop specific constraints to the production of sorghum, cowpea, maize, cotton, groundnuts and cassava. With regard to the soil induced limitations to crop production, unfavorable textural properties prevail, except for terrain components on gabbro or basaltic parent material. Unfavorable climatic conditions determine the suitability of this region for cotton, maize and cassava production. The ranking of the physical suitability of the six crops for Central Benin was in the order sorghum>groundnut>cowpea, cassava>maize>cotton. The problem of interannual variability of precipitation and its effects on the climatic suitability is discussed.