Farmers  in West Africa need to develop strategies for harvesting and conserving rainfall. West Africa is a semi-arid landscape with unreliable rainfall that limits agricultural yield and population stability. Many proven methods for optimizing use of rainfall have not been adopted here where they are potentially beneficial to those in need, even with incentives such as food-for-work applied. Ultimately, an un-incentivised return to a traditional and largely abandoned conservation practice has yielded positive results.

A practice known as Tassa and as zai has become increasingly popular in Nigeria and its popularity has spawned a new enterprise for day laborers who have mastered the technique. Tassa is a method of conserving water in small hand-dug pits, some 20-30 cm in diameter, 15-20 cm deep and 0.4-1.0 m apart. When a Tassa pit is created, the removed earth is placed on the downstream side of the pit to form a small ridge and to retain more water before it escapes as runoff. The pit bottoms are then covered with manure to provide nutrients and improve water infiltration and retention. When it rains, the holes fill with water and farmers plant millet or sorghum in them. Tassa pits take 50-60 working days per hectare to construct and about ten working days per hectare to maintain, depending on the soil and rainfall. They need redigging every one-to-three years.

The use of Tassa in Nigeria was instrumental in bringing a total of 4,000 ha back into production over the course of a few years. In surveys, farmers cited several reasons for this rapid uptake: doubling of yields, rehabilitation of barren land, easy maintenance and easy weeding and thinning.

Tassa is a simple, inexpensive and easily implemented method for conserving rainwater and regenerating soild for agriculture in areas experiencing unreliable rainfall and climate change.

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