Faidherbia albida is a tree of some consequence. As an important source of nitrogen in tropical agriculture, it is beginning to gain popularity in Africa. Not only able to access and make available to crops deeper sources of nitrogen, it sheds its leaves in the wet season and retains them in the dry season, acting as shade for crops without competing with them for light. Adoption in Niger and Zambia have been significant (4.8 million hectares and 300,000 hectares, respectively) and yield increases promising. At the Zambia Conservation Farming Unit unfertilised maize yields have increased to 4.1 tons per hectare from 1.3 t/ha when grown near F. albida trees. While in Malawi maize yields increased by 280% when grown in the zone of F. albida. There is another benefit too, carbon storage and accumulation. Tropical trees such as F. albida can sequester a minimum of 22.6 kg of carbon from the atmosphere each year.
But these trees are only one element of a wider movement, that of Evergreen Agriculture. Championed by the World Agroforestry Centre, Evergreen Agriculture combines the principles of Conservation Farming with agroforestry (both discussed in Chapter 13). The former, currently practiced globally on 100 million hectares of cropland, has direct benefits for soil and water conservation while the latter provides sources of green fertiliser, a diversity of products farmers can cultivate and other environmental benefits, such as shelter, erosion control and watershed protection. All of these combine to provide increased crop yields and a more stable, resilient farming system.
One Billion Hungry: Can We Feed the World? 