Origins of Zai
Around 1980, farmers in the village of Gourga, which is situated close to the regional capital Ouahigouya, started to experiment with traditional planting pits or zaï. The dimensions of the pits were increased (from a diameter of 10 – 15 cm to 20 – 30 cm and a depth of about 20 cm) and another innovation was that manure was applied to them. These termites play a crucial role as they dig channels in the soil and by doing so they improve its ‘architecture’. At the same time they digest the organic matter and make nutrients more easily available to the crops planted or sown in the pits.
Source: http://www.ifpri.org/divs/eptd/dp/papers/eptdp114.pdf