for National Geographic News
For one and a half decades, Johannes Mutisya, 54, a farmer in Kenya's Makueni district just east of Nairobi, has done what he could to eke out a living—but with little success.
He has bent wearily and scratched the dry, hardened earth, sprinkling a few maize or bean seeds and hoping for the best.
"These days we are only trying," Mutisya said, a distant look on his face.
"It is not like two decades ago and beyond, when people could be sure of bounty harvest after the rains."
Mutisya's situation is occurring across Africa, where farmlands are severely degraded and production is down.
African farmers on average apply only 10 percent of the soil nutrients, such as fertilizer, used in other parts of the world.
Coupled with effects of climate change, such as extreme droughts, the situation seems bleak.
But growing trees—especially acacia— on farms can improve the lot of some African farmers, said Dennis Garrity, who heads the Nairobi-based World Agroforestry Center.
Garrity spoke at the Second World Congress of Agroforestry held in Nairobi in August, which convened more than a thousand international experts to discuss the importance of growing trees on farms.
The tall, long-lived acacia tree Faidherbia albida could serve as a free source of long-lasting and crop-boosting nitrogen, Garrity said.
A nitrogen fixer, the tree species could limit the use of polluting chemical fertilizers while also providing animal feed, construction material, and even medicine for farmers across sub-Saharan Africa.
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