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 centimetres across and around 5 to 15 centimetres deep, spaced approximately 80 centimetres (3 ft) apart. The technique is traditionally used in western Sahel to restore degraded drylands and increase soil fertility. The technique has also been adopted by smallholder farmers in semi-arid regions of East Africa, particularly in Kenya, where farmers in counties such as Kitui use it in combination with modern agricultural practices to improve water retention and crop yields in dryland conditions.