Zaï

Zaï or tassa is a farming technique of digging pits in less permeable soil to catch water and concentrate compost. The pits are between 15 and 50 cm across and around 5 to 15 cm deep, spaced approximately 80 cm apart. The technique is traditionally used in western Sahel (Burkina Faso, Niger, Mali) to restore degraded drylands and increase soil fertility.

Zaï holes were reintroduced since the 1980s by Yacouba Sawadogo, a farmer from Burkina Faso, who introduced the innovation of filling them with manure and compost to provide plant nutrients. The manure attracts termites, whose tunnels help further break up the soil. He also slightly increased the size of the holes over the traditional models. Zaï holes help by improving the yields of trees, sorghum, and millet by up to 500 percent.

As an alternative to the zaï technique, some agricultural engineers suggest a diking technique, especially in the case of very light soils.