Responses of soil crusting, runoff and erosion to fallowing in the sub-humid and semi-arid regions of West Africa uri icon

abstract

  • Systems including a long fallow period have proven to be sustainable in the tropics for they enable the transfer of the rich store of nutrients from the vegetation to the ensuing crops. These systems have been mainly studied in the forest zone with a peculiar focus on the maintenance of organic and chemical fertility. By contrast, the effects of the fallow on soil physical properties have not been widely documented especially in the drier areas. The objectives of this paper are: (i) to summarise the fragmented and not readily accessible information on the responses of soil crusting, runoff, water and wind erosion to fallowing in the sub-humid and semi-arid regions of West Africa; (ii) to infer possible scenarios of land use change from the recent past. Two main examples have been taken in northern Ivory Coast and southern Niger. In the Ivorian example, physical properties are restored after a fallow duration of 10 years on sandy clay loam whilst crusts persist over a longer period on sandy soils, partly due to the foraging activities of termites. In the sandy Sahelian soils, cultivation destroys the erosion crusts that develop as the fallow proceeds as a result of dust deposition and colonisation by blue green algae. This crust development is inherent to the Sahelian ecosystem and favours the natural concentration of water resources. The net balance of dust is negative in millet fields (-0.25 t ha(-1) per year) and positive in young fallows (+0.68 t ha(-1) per year) so that a slight increase in the field/fallow ratio can transform the region from an accumulation zone to a source zone with consequences on regional fertility transfer. Finally, in both regions the sandy soils have specific dynamics that should be accounted in land management planning. Despite a higher water erosion risk, the sub-humid zone offers a better potential for intensification than the semi-arid zone. (C) 2004 Elsevier B.V. All rights reserved.

publication date

  • 2004
  • 2004
  • 2004