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More than half the land in the Sahelian zone are degraded with a hard crust on the surface. The first step in reclamation is to break up the crust and then dig out micro-catchments (called demi-lunes) to store run-off water, every five to ten metres. The dimension of the demi-lune varies but are recommended to be two-by-three metres.
Trees are planted in the centre of the open side of the demi-lune to avoid waterlogging. In the area between the demi-lunes, planting pits, commonly known as zai holes, are dug out. A zai is a 20 ? 20 ? 20 cm deep hole and infilled with about 250 g of compost or manure in the bottom and covered with soil. Traditional vegetables are then planted.
Putting the compost in the bottom of the hole encourages the plant to grow an extensive root system so that it can extract more moisture and nutrients. In addition trenches are dug every 20...