Transport of soil and nutrients by wind in bush fallow land and traditionally managed cultivated fields in the Sahel uri icon

abstract

  • In the West African Sahel, few direct measurements are currently available for the major land-use types on the extent of soil losses by wind erosion. A measurement campaign was therefore carried out in 1997 to monitor windblown sediment fluxes using Big Spring Number Eight (BSNE) sand-traps in a conventionally managed cultivated field and bush fallow in western Niger. Sediment balances were derived from the measured windblown sediment mass fluxes. Results indicate that sediment fluxes in a cultivated field increased linearly over distances up to 76 m irrespective of wind speed and duration. Sediment deposition over distances up to 47 m in an adjacent bush fallow was well described by an exponential decay function with a near constant trapping efficiency coefficient of 0.11 m?1 for incoming sediment mass fluxes between 10 and 45 kg m?1. Soil mass balances up to ?17.5 and +10.5 Mg ha?1 were measured in a single storm in the field and fallow, respectively. However, 89% of the sediment deposition observed in the fallow occurred within the first 20 m. The nutrient content of windblown sediment generally declined with distance into the field and increased with distance into the bush fallow. Because of the low nutrient content of the native soil, total nutrient losses remained very low (<163 mg m?2 for any given nutrient). However, such losses were by no means negligible compared to the average nutrient uptake by a millet crop. The present measurements confirm that wind erosion can result in substantial soil losses in traditionally managed fields on the sandy soil of the Sahel. The bulk of sediment transport is, however, predominantly short range as the saltating material is efficiently trapped by the natural vegetation of fallow land

publication date

  • 2002
  • 2002