Soil Tillage and Windbreak Effects on Millet and Cowpea: I. Wind Speed, Evaporation, and Wind Erosion

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Abstract
Deforestation, overgrazing, and declining soil regeneration periods have resulted in increased wind erosion problems in dry areas of the West African Sahel, but little is known about the bio‐physical factors involved. This research was conducted to determine the effects of ridging and four different windbreak spacings on wind erosion, potential evaporation, and soil water reserves. A field trial was conducted from 1985 to 1987 on 12 ha of a Psammentic Paleustalf in Southern Niger. Millet, Pennisetum glaucum (L.), and cowpea, Vigna unguiculata (L.) Walp., were seeded in strips on flat and ridged soil. Windbreaks of savannah vegetation were spaced at 6, 20, 40, and 90 m. The effects of ridging on wind speed, evaporation, and wind erosion were small and mostly non‐significant. However, average wind speed at 0.3 m above ground in the center of cowpea and millet strips was significantly reduced from 2.8 to 2.1 m s—1 as windbreak distances narrowed from 90 to 6 m. As a consequence, potential evaporation declined by 15% and the amount of wind blown soil particles by 50% in ridged and by 70% in flat treatments. Despite reduced potential evaporation, average subsoil water reserves were 14 mm smaller in the 6‐ than in the 20‐m windbreak spacing indicating excessive water extraction by the windbreak vegetation. Thus, establishing windbreaks with natural savannah vegetation may require a careful consideration of the agronomic benefits and costs to competing crops.

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