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December 09, 2008

Biochar as an alternative to synthetic fertiliser

On his farm in the hills of west virginia, Josh Frye isn't raising chickens just for meat. He is also raising them for their manure. Through a process that some scientists tout as a solution to climate change, food shortages and the energy crisis, Frye is transforming the waste into a charcoal-like substance called biochar that in the long run could be far better for the world than chicken nuggets. "It might look like this is just a poultry farm," says Frye. "But it's a char farm too."

Burn almost any kind of organic material — corn husks, hazelnut shells, bamboo and, yes, even chicken manure — in an oxygen-depleted process called pyrolysis, and you generate gases and heat that can be used as energy. What remains is a solid — biochar — that sequesters carbon, keeping CO2 out of the atmosphere. In principle, at least, you create energy in a way that is not just carbon neutral, but carbon negative.

And the benefits only begin there. When added to thin and acidic soil of the kind found in much of South America and Africa, char produces higher agricultural yields and lets farmers cut down on costly, petroleum-heavy fertilizers. Subsistence farmers seeking better soil have traditionally relied on slash-and-burn agriculture, which generates greenhouse gases and decimates forests. If instead those farmers slow-smoldered their agricultural waste to produce charcoal — in effect, slash-and-char agriculture — they could fertilize existing plots instead of clearing more land. This in turn would reduce emissions in the atmosphere, and so on in a virtuous circle of environmental renewal.

Could it really be that simple? It appears to have been for the original inhabitants of the Amazon basin. In the 16th century, Spanish explorer Francisco de Orellana wrote home describing the remarkably fertile lands he had discovered there. In the 19th century, American and Canadian geologists uncovered the reason: bands of terra preta (dark earth), which locals continued to cultivate successfully. Research revealed that the original inhabitants of the region had added charred wood and leaves — biochar — to their lands.

Centuries later, it was still there, enriching the soil. "You couldn't help but notice it. There would be all this poor, grayish soil, and then, right next to it, a tract of black that was several meters deep," says Johannes Lehmann, a soil scientist who worked in Manaus, Brazil, in the late 1990s. After he left the Amazon in 2000 for a job at Cornell University, N.Y., Lehmann started wondering what would happen if farmers today could make their own terra preta. He has found one answer in a field trial in Kenya, where 45 farmers achieved twice the yield in their corn crops with biochar than with conventional fertilizers.

Epidra, a private firm in Athens, Georgia, is exploring larger-scale applications, such as pyrolysis systems that can produce both enough energy to power a tractor and a biochar tailored to improve particular soils. "If you're going to grow food, you have to do it responsibly," says Bob Hawkins, Eprida's project manager. "And one way of doing that is to use it to generate sustainable energy." A prototype can turn a ton of ground peanut shells into 600 lb. (270 kg) of biochar, with energy as the bonus.

Biochar's ability to sequester CO2 has given new urgency to such research. "Reducing emissions isn't enough — we have to draw down the carbon stock in the atmosphere," says Tim Flannery, chair of the Copenhagen Climate Council, a consortium of scientists and business leaders linked to next year's United Nations Climate Summit. "And for that, slow pyrolysis biochar is a superior solution to anything else that's been proposed." Cornell's Lehmann is even more emphatic. "If biochar could be massively applied around the globe," he says, "we could end the emissions problem in one to two years."

Not everyone agrees. "Biochar isn't a silver bullet, not by a long shot," says Dominic Woolf, a researcher at Swansea University in Wales. "You have to look at the big picture: pyrolysis itself produces carbon dioxide emissions, and you have to consider that when you try to determine biochar's capacity for sequestration."

Lehmann says he welcomes the doubts, and notes that addressing them requires "investors willing to take the risk." Which is where chicken farmer Frye, with his small biochar operation, comes in as one of the few people out there actually making a business of it. With a pyrolysis unit that can create 3-4 tons of biochar a day, he generates enough energy to heat his hen houses; and he sells the char as fertilizer for $600 a ton. For Lehmann, biochar's benefits aren't so much a scientific novelty as a return to basics. "From cave drawings to iron smelting, charcoal has always played an important role in the development of civilization," he says. "Maybe it's about to do it again."

Time

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