Effects of Wind Erosion On Water Balance in a Crop Field in the Sahel, West Africa.

Desertification is caused by wind erosion in the Sahel. However, its mechanism has not been fully understood. In our previous study, it was revealed that 4-5 mm of surface loose layer was removed every year from a crop field by wind erosion, resulting in the exposure of soil crust on the soil surface. In this study, we examined the effects of soil surface status on the water balance in a crop field using the lysimeter in the ICRISAT West and Central Africa. We used three lysimeters (2 m in diameter, 2 m deep) with different soil surface status (i.e., 0, 3, or 7 cm of loose layer was laid on the soil crust). Plots with 0, 3, and 7 cm of loose layer can be considered eroded field, uneroded field, and field which trapped eroded soil, respectively. In the rainy season of 2011, pearl millet (Pennisetum glaucum) was planted in the lysimeters. We measured rainfall amount and runoff in each event, drainage volume (at 200 cm deep) everyday, and soil water content (0-200 cm) in every 10 min. Annual rainfall was 440 mm in 2011. The most remarkable effect of soil surface status on the water balance was found in soil permeability. In the plot where soil crust was exposed, runoff ratio was 45 %, whereas it was only 9% and 5% in the plots with 3 and 7 cm of loose layer, respectively. This result suggested that the exposure of soil crust can easily create drought condition in the soil because minimum soil water required for pearl millet production was estimated to be 270 mm. One of the major processes of desertification by wind erosion in the Sahel will be the exposure of soil crust which results in deterioration of soil permeability.