Science: Smoking Grass

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

By Ben Whitford

Photo by Mingxin Guo and students, Deleware State University

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 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 com­bat 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, transport, and bury biochar could outweigh the carbon savings. Even biochar’s fans admit it’s a work in progress: Scientists don’t know how much charcoal farmers should use, how they should apply it, or which feedstocks work best. “We just don’t know enough about it yet,” says recently retired USDA scientist John Kimble. “It’s got potential, but it’s going to take a lot more work.”

The biggest barriers, though, are economic. With farmers reluctant to spread unproven products on their fields, the few companies manufacturing biochar have struggled to find buyers. Dynamotive, a Vancouver-based energy company, simply gives it away to farmers willing to try it. “The market for biochar is basically nonexistent,” admits Desmond Radlein, one of the company’s directors.

Analysts say that won’t change until carbon markets are established, allowing farmers to earn credits for applying biochar to their fields. “People aren’t going to invest until they can show they’ll get a return on their investments,” says Debbie Reed, coordinator of the International Biochar Initiative, a nonprofit working to promote the commercialization of the fertilizer. Still, lawmakers hope to jump-start the industry. The current Farm Bill contains several high-priority research programs for which $10 million per year is authorized for biochar studies, and the Senate is considering a $500 million grant program. “There’s been a paradigm shift at the highest policy levels,”

Reed says. If that’s true, it could just be a matter of time until the biochar industry hits pay dirt.

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Issue 25

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