Black Gold of the Amazon

Fertile, charred soil created by pre-Columbian peoples sustained surprisingly large settlements in the rain forest. Secrets of that ancient “dark earth” could help solve the Amazon’s ecological problems today

…Creating new terra preta in the Amazon today would have several advantages, Lehmann says. First, because the enriched soil remains fertile for a long time, its use would discourage farmers from moving on and burning more forest to open up new fields. Second, because of the added charcoal, terra preta holds up to 10 times as much carbon as unaltered soils. The late W’s Sombroek – a legendary soil scientist whose long interest in terra preta earned him the epithet “the godfather of dark earth” – began to wonder if dark earth could be used to sequester carbon. Lehmann’s studies have shown that it can: Fifty percent of the original carbon in plants and trees used to make biochar remains in the terra preta soils after the conversion.

What does this mean for fighting global warming? Brazil is the world’s eighth-largest emitter of greenhouse gases, and most of those emissions come not from industry and cars but from loggers, ranchers, and farmers burning the forest. Just substituting slash-and-char for slash-and-burn could reduce human-produced carbon emissions in the Amazon by 12 percent.


Even better, burning agricultural wastes in a controlled process called pyrolysis can convert wood and other organic waste into useful volatile gases, heat, electricity, and bio-oil. The process is win-win: Burning the biomass produces substantial amounts of rich biochar from waste material like peanut shells and rice husks, and mixing this biochar into soil could more than offset the carbon that is emitted into the atmosphere-not only during the burning process itself, but also when the derived fuels are used.

“You wouldn’t just be carbon neutral, you would be carbon negative, drawing carbon dioxide out of the atmosphere, producing energy and improving the climate in the process,” Lehmann says.

Discover