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Unique Acacia Tree’s Promise To Revive African Soils
ScienceDaily (Aug. 26, 2009) — Scientists said at the 2nd World Congress of Agroforestry that a type of acacia tree with an unusual growth habit-unlike virtually all other trees-holds particular promise for farmers in Africa as a free source of nitrogen for their soils that could last generations.
With its nitrogen-fixing qualities, the tall, long-lived acacia tree, Faidherbia albida (Mgunga in Swahili) could limit the use of fertilizers; provide fodder for livestock, wood for construction and fuel wood, and medicine through its bark, as well as windbreaks and erosion control to farmers across sub-Saharan Africa. The tree illustrates the benefits of growing trees on farms, said the scientists at today’s meeting, and is adapted to an incredibly wide array of climates and soils from the deserts to the humid tropics.
“The future of trees is on farms,” said Dennis Garrity, Director General of the World Agroforestry Centre, or ICRAF, one of 15 centers supported by the Consultative Group on International Agricultural Research (CGIAR). The Center is hosting the Congress, which has convened about 800 global experts to discuss the importance of growing trees on farms for humanity’s survival.
“Growing the right tree in the right place on farms in sub-Saharan Africa-and worldwide- has the potential to slow climate change, feed more people, and protect the environment. This tree, as a source of free, organic nitrogen, is an example of that. There are many other examples of solutions to African farming that exist here already.”
African farmland is severely degraded and African farmers, on average, apply only 10 percent of soil nutrients used in the rest of the world. Low-cost options are critical to reversing the continent’s declining farm productivity, the scientists said, as sharply increasing fertilizer prices further limit the choices African farmers have to improve farm yields while protecting forests from further clearing.
The Faidherbia acacia tree has the quality of “reverse leaf phenology,” which drives the tree to go dormant and shed its nitrogen-rich leaves during the early rainy season-when seeds are being planted and need the nitrogen-and then to re-grow its leaves when the dry season begins and crops are dormant. This makes it highly compatible with food crops because it does not compete with them for light-only the bare branches of the tree’s canopy spread overhead while crops grow to maturity. Their leaves and pods provide a crucial source of fodder in the dry season for livestock when other plants have dried up.