SOIL CHARACTERIZATION IN A SEMI-ARID VALLEY: THE CASE OF SOILS UPSTREAM OF THE WEDBILA DAM IN BURKINA FASO

In intermittent river valleys where land seems more fertile, agricultural producers settle around for production. In arid and semi-arid zones, the scarcity of rainfall combined with its uneven spatio-temporal distributions, coupled with the advanced state of land degradation significantly reduce crop yields. Also, the lack of knowledge of the physico-chemical characteristics of soils by farmers does not allow a rational and sustainable use of the land. However, knowledge of soil characteristics is a sine qua none way to solve this problem. This knowledge is also necessary to assess soils in their role as a stock and transfer of water to groundwater. To contribute to the knowledge of soils upstream of the Wedbila dam in Burkina Faso, we analyzed the recommended physical and chemical parameters for soils such as conductivity at saturation and bulk density measured in situ, cation exchange capacity, organic matter measured in the laboratory with conventional methods. We also analyzed the evolution of the moisture content over a nine-month period. Open profiles showed tropical ferruginous dominated soils leached with spots and concretions as well as ferruginized eutrophic brown soils. Monitoring the evolution of soil moisture shows that the water stock is at its maximum during the winter period. Sudden variations are observed at the beginning of wintering and desaturation could be explained by the coarse texture of the surface soils caused by the leaching of clays either by evaporation or drainage to the lower horizons. The latter is still low compared to the density and infiltration coefficient in these layers. The density of the soils varies between 1.5-1.8g/cm 3 and the average infiltration rate is of the order of 10-6 indicating a finer or clayey texture of the soils. Soils are acidic although organic matter contents are average in the first 30 centimeters and have a low cation exchange capacity. This situation considerably compromises the structural and textural stability of these soils and therefore their productivity. The presence of many pores is an asset for a good percolation of water to the groundwater that could be used for complementary agriculture in the dry season. Available data on soil characteristics will guide producers to adopt appropriate management systems and ensure sustainable soil management.