The article highlights some important nuances. Terra mulata, the lighter type of terra preta, covers much more area than the celebrated black type central to the concept of terra preta.

Why people living on hills overlooking many rivers in Brazil two millennia ago devised this approach is still a subject of debate, as is how they added all the extra organic content and ensured the soil was teeming with beneficial bugs and other micro-organisms. A modern technology called low-temperature pyrolysis can produce bio-char on an industrial scale. Using wood or agricultural wastes for fuel, pyrolysis would generate heat for electricity while also actually reducing net emissions of carbon dioxide since the organic matter would otherwise decompose. "This might be the beginning of a bio-char revolution," Lehmann says.

Applying the knowledge of terra preta to contemporary soil management can decrease the amount of fertilizer needed, because bio-char helps retain nitrogen in the soil as well as higher levels of plant-available phosphorus, calcium, sulfur and organic matter. The black soil also does not get depleted, as do other soils, after repeated use. Producing and applying bio-char to soil would not only dramatically improve soil and increase crop production, but also could provide a novel approach to establishing a significant, long-term sink for atmospheric carbon dioxide.