Zaï or tassa is a farming method that involves digging small pits in soil that does not let water pass through easily. These pits are between 15 and 50 centimeters (0.5 to 2 feet) wide and about 5 to 15 centimeters (2 to 6 inches) deep. They are placed roughly 80 centimeters (3 feet) apart. This technique is often used in the western Sahel region, including Burkina Faso, Niger, and Mali, to improve dry, damaged land and make the soil more fertile.

Since the 1980s, a farmer named Yacouba Sawadogo from Burkina Faso helped reintroduce zaï holes. He filled them with manure and compost to add nutrients for plants. The manure attracts termites, which create tunnels that help loosen the soil. He also made the holes slightly larger than traditional designs. Zaï holes can increase the growth of trees, sorghum, and millet by up to 500%.

An alternative to zaï is a diking technique, which some agricultural engineers recommend for very light soils.