Evergreen Agriculture - the combination of trees in farming systems (agroforestry) with the principles of conservation farming - is emerging as an affordable and accessible science-based solution to caring better for the land and increasing smallholder food production.
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The most promising results in Evergreen Agriculture are coming from the integration of fertilizer trees into cropping systems. These trees improve soil fertility by drawing nitrogen from the air and transferring it to the soil through their roots and leaf litter. Scientists have been evaluating various species of fertilizer trees for many years, including Sesbania, Gliricidia and Tephrosia. Currently, Faidherbia albida is showing promise as the possiblecornerstone of Evergreen Agriculture in the future for the tropics.
This indigenous African acacia is already a natural component of farming systems across much of the continent. Unlike most other trees, Faidherbia sheds its nitrogen-rich leaves during the early rainy season and remains dormant throughout the crop-growing period: the leaves grow again when the dry season begins. This makes it highly compatible with food crops, because it does not compete with them for light, nutrients, or water during the growing season: only its bare branches spread overhead while the food crops grow to maturity.
In Zambia, more than 160,000 farmers have extended their conservation farming practices to include the cultivation of food crops within agroforests of Faidherbia trees over an area of 300,000 hectares. Zambia’s Conservation Farming Unit has observed that unfertilized maize yields in the vicinity of Faidherbia trees averaged 4.1 t/ha, compared to 1.3 t/ha nearby but beyond the tree canopy.
http://www.worldagroforestry.org/evergreen_agriculture