A farmer in Mile One (Cameroon) shows the difference between the roots of a maize plant grown in biochar (left) and the roots of the same plant grown in bare soil. Photo credit: Laurens Rademakers, Etchi Daniel-Jones.

Terra preta (“black soil” in Portuguese) is dark, incredibly fertile soil found in the Brazilian Amazon basin. These soils were created by humans between 450 BC and AD 950; it is now widely accepted that terra preta soils are a product of indigenous soil management involving a labor-intensive technique called “slash and char” (as opposed to “slash and burn”). Through this process, the seasonal crop residue was charred and turned into the earth. This sequestered most of the carbon in the crop residue, and created an extremely hospitable amendment to the otherwise thin and fragile soil – something that in turn nurtured beneficial microorganisms, which broke down the poor native soil and transformed it into extraordinarily rich humus.

Soil analysis suggests that original ingredients included:

• Human and animal excrements (rich in phosphorus and nitrogen);
• Kitchen refuse, such as animal bones (rich in phosphorus and calcium);
• Ash residue from incomplete combustion (rich in calcium, magnesium, potassium, phosphorus and charcoal);
• Biomass of terrestrial plants (e.g. compost); and
• Biomass of aquatic plants (e.g. algae).

Charcoal (aka biochar or agrichar) is believed to be the key ingredient in the formation of terra preta.

Researchers have theorized that terra preta covers at least 10 percent of Amazonia, an area the size of France, and that these deposits regenerate themselves at a rate of 3/8 inch (1 centimetre) per year. Terra preta is used and sold as quality compost by local farmers and businesses.

Internationally, there has been a surge of interest in the last year in biochar as both a commercial venture and an academic challenge. Biochar manufacturing presents the potential benefits of carbon sequestering and the creation of liquid fuel as a by-product. The controlled production of terra preta soil has excited manufacturers, researchers, anthropologists, as well as social and environmental activists seeking solutions for world hunger, soil depletion and desertification. Attempts to recreate terra preta soils are underway worldwide.

Since December 2008, more than 1,500 subsistence farmers in Cameroon’s South-West Region have been participating in the largest-ever field trial testing the effects of biochar on crop productivity. The first results of this ongoing experiment, based on maize planted in a large series of plots, are now available. The data demonstrates how biochar consistently helps to boost crop productivity in tropical soils, sometimes in a spectacular manner. The preliminary results suggest that biochar may offer a solution to hunger and food insecurity amongst the world’s poorest, as well as to soil depletion and tropical deforestation. For more information, visit www.biocharfund.org.