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Scientist Mingxin Guo has shown that biochar-infused soil vastly improves winter wheat growth rates compared to regular soil.

Smoking Grass An ancient technique for enriching soil could revolutionize farming and curb climate change

photo by Mingxin Guo and students, delaware state university


n 1542, Spanish conquistador Francisco de Orellana returned from the New World with tales of bustling cities lining the banks of the Amazon River. “They have a great wealth of gold and silver,” wrote his chronicler, “and great cities of white stone glistening in the sun.” But when missionaries retraced Orellana’s steps a century later, they found no sign of the settlements he’d described. Even the soil seemed to contradict his claims; it was yellowish and barren, apparently incapable of sustaining more than a few scattered bands of hunter-gatherers. Lately, though, researchers have realized that Orellana might have been telling the truth. It turns out that the Amazon basin is dotted with patches of rich, black loam known as terra preta del Indio, or “Indian dark earth.” Studies show that these soils, which Indian farmers created by mixing charcoal and fish bones into their fields, can be almost nine times more fertile than unaltered earth and could once have fed tens of millions of people. “There are hundreds of thousands of these patches,” says William Woods, a University of Kansas geographer. “The implication is that there were a lot of people in pre-Colombian Amazonia sustainably producing food.” There might be a lesson here for modern farmers. The recipe for terra preta was lost long ago, but in theory, its effects could be replicated by sowing fields with biochar, a type of charcoal. By fixing nutrients in place

Farmers who use biochar could actually help combat global warming. and altering the soil’s microbial balance, biochar could boost crop yields and reduce the need for chemical fertilizers. The early signs are promising: Mingxin Guo, a soil scientist at Delaware State University, recently found that wheat grown in charcoal-spiked soil yielded 45 percent more biomass. “With a one-off addition, the soil quality appears to be permanently improved,” he says. The real payoff, though, is that farmers who use biochar could actually help com­ bat global warming. All plants absorb carbon dioxide as they grow; ordinarily, that greenhouse gas is released when the plants decompose. But converting plants into charcoal can stabilize their carbon: While plants store carbon for months or years, biochar can trap it for hundreds or even thousands of years. According to Robert Brown, director of Iowa State University’s Center for Sustainable Environmental Technologies, charring half the crop residues from one square mile of farmland would lock

away enough carbon to offset the emissions from 330 automobiles. What’s more, when plants are charred, they give off fumes that can be condensed into a carbon-negative bio-oil capable of powering an auto engine. A handful of companies are already producing fuel from this organic waste. Johannes Lehmann, a biochar specialist at Cornell University, calculates that by the end of the century, bio-oil and biochar production could sequester 9.5 billion metric tons of carbon a year—more than enough to offset all global fossil-fuel emissions today. That’s especially exciting, Lehmann says, because unlike biodiesel and corn ethanol, biochar doesn’t take land away from food production. “We can simply use material we don’t need, like crop residues or waste products,” he says. “This has humongous potential.” There’s a downside, of course. Careless charcoal production can generate toxic waste, and the energy needed to produce, | 33

Plenty Magazine Issue 23 Aug/Sept 2008  

beyond the bulb> the best Ideas In green desIgn krIstIn gore kIlls her laWn | saIlIng greece | gossIp gIrl’s eco star

Plenty Magazine Issue 23 Aug/Sept 2008  

beyond the bulb> the best Ideas In green desIgn krIstIn gore kIlls her laWn | saIlIng greece | gossIp gIrl’s eco star