Unlike ordinary tropical soils, terra preta remains fertile after centuries of exposure to tropical sun and rain, notes Wenceslau Teixeira, a soil scientist at Embrapa, a network of agricultural research and extension agencies in Brazil. Its remarkable resilience, he says, has been demonstrated at Embrapa's facility in Manaus, where scientists test new crop varieties in replica patches of terra preta. "For 40 years, that's where they tried out rice, corn, manioc, beans, you name it," Teixeira says. "It was all just what you're not supposed to do in the tropics—annual crops, completely exposed to sun and rain. It's as if we were trying to ruin it, and we haven't succeeded!" Teixeira is now testing terra preta with bananas and other tropical crops.
Sombroek had wondered if modern farmers might create their own terra preta—terra preta nova, as he dubbed it. Much as the green revolution dramatically improved the developing world's crops, terra preta could unleash what the scientific journal Nature has called a "black revolution" across the broad arc of impoverished soil from Southeast Asia to Africa.
Key to terra preta is charcoal, made by burning plants and refuse at low temperatures. In March a research team led by Christoph Steiner, then of the University of Bayreuth, reported that simply adding crumbled charcoal and condensed smoke to typically bad tropical soils caused an "exponential increase" in the microbial population—kick-starting the underground ecosystem that is critical to fertility. Tropical soils quickly lose microbial richness when converted to agriculture. Charcoal seems to provide habitat for microbes—making a kind of artificial soil within the soil—partly because nutrients bind to the charcoal rather than being washed away. Tests by a U.S.-Brazilian team in 2006 found that terra preta had a far greater number and variety of microorganisms than typical tropical soils—it was literally more alive.
A black revolution might even help combat global warming. Agriculture accounts for more than one-eighth of humankind's production of greenhouse gases. Heavily plowed soil releases carbon dioxide as it exposes once buried organic matter. Sombroek argued that creating terra preta around the world would use so much carbon-rich charcoal that it could more than offset the release of soil carbon into the atmosphere. According to William I. Woods, a geographer and soil scientist at the University of Kansas, charcoal-rich terra preta has 10 or 20 times more carbon than typical tropical soils, and the carbon can be buried much deeper down. Rough calculations show that "the amount of carbon we can put into the soil is staggering," Woods says. Last year Cornell University soil scientist Johannes Lehmann estimated in Nature that simply converting residues from commercial forestry, fallow farm fields, and annual crops to charcoal could compensate for about a third of U.S. fossil-fuel emissions. Indeed, Lehmann and two colleagues have argued that humankind's use of fossil fuels worldwide could be wholly offset by storing carbon in terra preta nova.
Such hopes will not be easy to fulfill. Identifying the organisms associated with terra preta will be difficult. And nobody knows for sure how much carbon can be stored in soil—some studies suggest there may be a finite limit. But Woods believes that the odds of a payoff are good. "The world is going to hear a lot more about terra preta," he says.