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Summary Band 41

Junge, Birte: The soils in the catchment of the Upper Ouémé in Benin/West Africa - soil genesis, classification, land use and degradation -. Bonner Bodenkundl. Abh. 41 (2005), 291 S.

 

In the work, the soils developed in the catchment of the Upper Ouémé are characterized and their degradation in the current low input land use system is pointed out. Furthermore, possibilities of a sustainable land use are discussed to achieve the conservation of the resource.

The soils developed in the undulating pediplain in the centre of Benin are characterized by the layering of fine grained and gravely substrates over saprolite. Sols ferrugineux tropicaux lessivés or Acrisols dominate on the slopes, whereas Sols hydromorphes peu humifères or Gleysols are distributed in the valleys, the bas-fonds. The natural fertility of these soils is low according to LANDON (1984), the Fertility Capability Classification System (FCC) of SANCHEZ et al. (1982) and the Framework for Land Evaluation (FAO 1976, 1981). Some reasons for the low suitability of the soils for plant production are the low field capacity, the low exchange capacity for nutrients, the limited rooting space and the water logging of the bas-fonds during the rainy season.

Traditionally, cereals like maize or sorghum and yam are cultivated on the soils without any fertilizer for self-sufficiency. Because of intensified land use due to the increasing population and the shortening of the fallow period which is important for the rehabilitation of the soils, different kind of soil degradation take place. Soil erosion by run off has already led to the reduction of the top surface layer. Furthermore, land use has deteriorated the soil structure due to the low cover of the soil surface and the low density of the crops which favour soil erosion. Soil loss, bush fire, harvesting and the shortening of the fallow period lead to the decrease of organic matter and nutrients which means the chemical deterioration of the soils. The population density of earthworms and their activity are decreased on agricultural used fields which are also biologically deteriorated.

To counteract soil degradation and to preserve the resource for further generations, the modification of the traditional land use system by different measures of plant cultivation and the use of fertilizer are necessary.

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