For hundreds of years, parts of sub-Saharan Africa have suffered from poor soil. Weather, shifting populations, and slash-and-burn practices have left wide swaths of land relatively useless for growing food without major commercial intervention. But that’s not the whole story of African farming.

In Guinea and the forests of West Africa, there is a hidden history of enriching the soil with natural techniques handed down through generations to sustain food crops without artificial fertilizers. And there just might be something the rest of the world can learn from it.

“The capacity of people to make soils where soils weren’t good … [has been] completely overlooked,” says James Fairhead, professor of social anthropology of Sussex University. That is, until now.

Fairhead, who has been exploring settlements in the forests of West Africa since the 1990s, had for years observed locals planting crops on the grounds of former villages. As an archaeologist digging for historic artifacts in the same locations, it could be something of a nuisance, he acknowledges, but he started to wonder why it was happening.

View Images On the left, the black, fertile soil dubbed African Dark Earths. On the right, the clay-like and nutrient poor soil common in sub-Saharan Africa. Photograph by Dawit Solomon, Cornell University

He looked for scientific literature on African soils and turned up nothing until he stumbled upon a similar discovery of soil improvement in the Amazon as far back as 5,000 years ago.

Taken together, these could be a “model for sustainable farming and a model for climate smart agriculture,” he says. (See "How Chickpeas Can Fix Soil and Feed Farmers".)

Fairhead and his colleagues analyzed 150 sites in northwest Liberia and 27 sites in Ghana and discovered that the enriched soils, dubbed “African Dark Earths,” contain 200 to 300 percent more organic carbon than nearby soils and can support more intensive farming. They also contain 2 to 26 times greater amounts of pyrogenic carbon, which persists longer in soil than other carbons and is important for soil fertility.

They published a paper recently in the journal Frontiers in Ecology and the Environment on their findings, noting that these methods of soil enrichment may offer a model for the future of agricultural carbon sequestration.

Once Fairhead started looking for it, he saw African Dark Earths in many places on the continent.

Village farmers are drawn to old ruins ripe with the detritus of people and animal waste, and charred remains of plants and trees, he says. To further improve the soil, they keep goats and chickens in specific areas, and bring food waste like byproducts from processing palm oil, bones, and palm thatch there to burn. These activities turn poor, heavy soil into a dark, nutritious plant medium, which is used judiciously by the communities.

Crops grown in this soil account for a large proportion of household income yet are spread only on small amounts of land, the study notes. (See "African Diet, Jobs Will Be Hit Hard by Climate Change".)

Dawit Solomon, a soil scientist at Cornell University and a co-author of the paper, says village elders talk about soil enrichment as if it’s the obvious thing to do, yet no one had ever asked them about it before. “The black soil was not here when people settled there. They always associate the age of their town with the depth of the black soil,” Solomon says.

The soils were most commonly used to grow food used in home gardens, including cassava, taro, and plantain.

The study is intriguing, soil scientists say.

“It is a neat example of traditional practices transforming soil properties to improve agriculture,” says Timothy Crews, ecologist and research director at the nonprofit research center, The Land Institute, who was not involved in the study.

“But," he adds, “the spatial extent of the soil transformation is very limited … and it must be so, because the transformation occurs (increasing pH and soil organic carbon) by concentrating organic matter or stuff that was organic matter (i.e., ash) in space—from an extensive landscape to intensive gardens.”

“So it is sort of robbing Peter to pay Paul because the soils where the organic matter originated do NOT received the organic materials back,” Crews says.

But, he notes, the African dark soils are particularly robust.

And in a world where two million go hungry and climate change looms on the horizon, finding new and old wasys to enrich the soil is increasingly important.