Faidherbia albida is a nitrogen-fixing Acacia tree that is widespread throughout Africa, growing in a variety of soils and climates. Faidherbia is able to make large quantities of nitrogen available to nearby crops and increase the store of carbon above ground and in the soil. It sheds its leaves in the wet season and retains them in the dry season, allowing for light to pass through in the wet season whilst providing residue in the dry season. As a consequence it is possible to plant and grow maize under the trees. Yields can reach more than 3 tonnes per hectare without fertilisers, depending on the amount of nitrogen fixed by the trees. The trees also contribute 2 tonnes or more of carbon per hectare to the soil and mature trees can store more than 30 tonnes of carbon per hectare.
In Malawi, Faidherbia provided 300kg of fertiliser per hectare and boosted unfertilised maize yields from 2.5-4 tonnes per hectare, 200% to 400% more than national averages, when planted every 10 rows. In a survey of 300 farmers in the Dedza district of Malawi, those that grew Faidherbia did so in order to improve soil fertility on their farms (starting when the trees are 4 to 6 years old), did not use nitrogen fertiliser and were keen to grow more trees. In Niger, Faidherbia has been planted on almost 5 million hectares of land leading to similar benefits.
The climate change mitigation potential for systems incorporating trees with fertilising properties lies in their ability to sequester between 2 and 4 tonnes of carbon per hectare per year, compared with 0.2-0.4 tonnes of carbon per hectare per year under conventional conservation farming systems. However, Faidherbia trees take 6 years to fully develop, making investments hard to justify, particularly if land tenure is insecure and/or farmers are dependent on immediate benefits and incomes. At present Faidherbia is grown on only 2% of Africa’s maize area and 13% of sorghum and millet area.