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

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 À 1 for incoming sediment mass fluxes between 10 and 45 kg m À1. Soil mass balances up to À17.5 and +10.5 Mg ha À1 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 À2 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.

Measurement and data analysis methods for field‐scale wind erosion studies and model validation

“…Saltation flux was near maximum at a distance of 250 m in a bare, fine sandy loam soil with small tillage ridges (Stout and Zobeck, 1996). Smaller fields may be adequate in sandier soils, although in a study of a sandy soil in Niger (greater than 90 per cent sand), the transport capacity was not reached at 80 m (Bielders et al, 2002).…”

Size resolved dust emission fluxes measured in Niger during 3 dust storms of the AMMA experiment

“…They may alter it also indirectly by favoring cloud formation (Levin et al, 1995). In semi-arid areas that are already poor in soil-nutrients the loss of fine dust that is naturally enriched in them (Bielders et al, 2002) can promote desertification. At the other end of the dust cycle, input of mineral particles in deposition areas can enhance the development of terrestrial or marine ecosystems (Swap, 1992;Jickells et al, 2005).…”

“Fallow Band System,” a land management practice for controlling desertification and improving crop production in the Sahel, West Africa. 1. Effectiveness in desertification control and soil fertility improvement

“…Topsoil, which typically contains more nutrients than subsoil, is detached and removed from arable land by wind. Thus, wind erosion affects the soil nutrient level (Daniel and Langham 1936;Zobeck and Fryrear 1986;Sterk et al 1996;Larney et al 1998;Bielders et al 2002) and soil productivity (Lyles 1975;Larney et al 1998). Moreover, abrasion and burial by the wind-blown sand can damage pearl millet stands (Pennisetum glaucum (L.) R.…”