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Acacia tree's promise to revive African soils
Scientists announce unique acacia tree's promise to revive African soils
Illustrates farm-boosting power of trees, say scientists
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
hosted the Congress, which 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.
Research on the tree began over 60 years ago when scientists observed that
farmers throughout the Sahelian region of Africa were retaining the trees in
their sorghum and millet fields. It is a frequent component of farming systems
of Senegal, Mali, Burkina Faso, Niger, Chad, Sudan, and Ethiopia, and in parts
of northern Ghana, northern Nigeria, and northern Cameroon. The tree is growing
on over 4.8 million hectares of land in Niger. Half a million farmers in Malawi
and in the southern highlands of Tanzania grow the tree on their maize fields.
In Malawi, maize yields were increased up to 280 percent in the zone under
the tree canopy compared with the zone outside the tree canopy. In Zambia,
recent unpublished observations showed that unfertilized maize yields in the
vicinity of the Faidherbia trees averaged 4.1 tonnes per hectare, compared to
1.3 tonnes nearby but beyond the tree canopy. Yield increases have also been
documented in unfertilized millets grown under the tree in West Africa, for
sorghum in Ethiopia, other parts of Africa, and in India, in addition to
groundnuts and cotton. Often, millet and sorghum exhibit no further response to
artificial fertilizers beyond that provided by the tree's leaf fall.
Currently, the Departments of Agriculture in both Malawi and Zambia are
seeking to double maize production with the use of the tree. They recommend that
farmers establish 100 Faidherbia trees on each hectare of maize that is planted.
Scientists at the conference noted some 700 published references to the
tree's history, ecology, and growing habits. "Knowledge of this tree is
farmer-driven," said Garrity. "We are now combining the scientific knowledge
base with the farmer knowledge base. There is sufficient research on both sides
to warrant dramatically scaling-up the planting of this tree on farms across
Africa through extension programs. The risks to farmers are low; it requires
very little labor, and delivers many benefits."
"Thus far we have failed to do enough to refine, adapt and extend the unique
properties of these trees to the more than 50 million food crop farmers who
desperately need home-grown solutions to their food production problems," he
continued.
More information:
 World Agroforestry
Centre (ICRAF)
The World Agroforestry Centre, based in Nairobi, Kenya is the world's leading
research institution on the diverse role trees play in agricultural landscapes
and rural livelihoods. As part of its work to bring tree-based solutions to bear
on poverty and environmental problems, centre researchers—working in close
collaboration with national partners—have developed new technologies, tools and
policy recommendations for increased food security and ecosystem health.
- ICRAF
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