Soil erosion and conservation in West Africa

Abstract

In context of the present chapter, West Africa is defined as the region lying between 0° N, 18° E and 18° N, 30° E. The region has an annual rainfall ranging between 300 and 3000 mm received in one or two distinct seasons. Alfisols are the predominant soils of the West African Savanna region with a rainfall of 800 to 1500 mm. The West African Alfisols are derived from crystalline acid rocks and basement complex and are usually characterized by a gravelly horizon at shallow depths. These soils have a coarse-textured surface horizon and are highly prone to compaction and erosion by water. About 60% of the West African Savanna is covered by Alfisols. Soils of the drier climate (300–800 mm annual rainfall) are mostly Aridisols, Inceptisols, and Alfisols. These soils are also susceptible to accelerated erosion. Ultisols and Oxisols occur in high rainfall (> 1500 mm annual rainfall) regions of West Africa, i.e. the coastal areas of the Ivory Coast, Liberia, Sierra Leone, eastern Nigeria and Cameroon. Some soils of central Africa now classified as Oxisols may, in fact, be Ultisols. Oxisols are predominant soils of the equatorial zone with high annual rainfall exceeding 2000 mm. Productivity potential of soils of West Africa is low because of low inherent fertility, low plant-available water reserves, variable and erratic rainfall, and severe erosion and erosion-caused degradation. How serious is soil erosion in West Africa? Soil erosion is severe in most areas of West Africa, especially where the natural vegetation cover has been removed toward an attempt to introduce food crop farming. In general, soil erosion is the most severe in savanna regions with an annual rainfall of 500 to 1000 mm. In the forest region, soil erosion becomes severe when the natural vegetation cover is removed.