While scientists around the world sweat the steady growth of climate change, Professor Johannes Lehmann, crop and soil sciences, and his researchers have turned up the heat to produce biochar – a fine-grained residue that may simultaneously improve soil health and curb harmful greenhouse gas (GHG) emissions.
Biochar is the organic matter left over after pyrolysis—a slow-burn conducted in the absence of oxygen. This process confines much of the carbon that might otherwise contribute to the formation of carbon dioxide, a prevalent GHG.
There is always a small amount of carbon emitted, said Thea Whitman grad. However, since it is done in the absence of oxygen, pyrolysis sequesters a considerable amount of carbon in the char itself. A 2007 study authored by Lehmann suggests that as much as 50 percent of the carbon originally present in the biomass may be retained in the biochar.
Physically, Lehmann said, biochar looks identical to burned material. Chemically, however, it is very different. "This doesn't mean it's not degrading, but it's degrading much more slowly," sometimes by up to two orders of magnitude, he said.
What this means for small farmers, said Charles Hyland grad, is not just better harvests for one season, but higher yields for life. "If you apply grass clippings or fallen leaves to a garden, it's not something that will persist [year after year]," he said. On the other hand, naturally occurring soils with char have existed in the Amazon for almost a thousand years and they are still fertile today.
"What is so thrilling about pyrolysis technology is that you do not have to sacrifice carbon sequestration for waste management,” researcher Kelly Hanley said. “With pyrolysis, it is a win-win situation."
Lehmann's lab, Hanley said, is currently looking for waste sources, such as yard clippings and animal manure, that may be used for char production in New York State. Lehmann's research also suggests that the application of biochar improves soil health by increasing nutrient retention and promoting microbial population growth.
In developing countries where soil quality is low, said Shelby Rajkovich '10, who works in Lehmann's lab, this represents an opportunity to lessen poverty for small farmers. "Theoretically," she said, "small farmers can produce their own biochar from their waste…at a low cost, which alleviates the financial stress on them to buy expensive inputs."
With healthier soils, Hanley explained, farmers can produce more with their land without relying on costly fertilizers and other off-site inputs.
But all char is not created equal. In addition to biochar, pyrolysis produces heat and a gas commonly referred to as syngas. The rate of the reaction and the material being burned (feedstock) determine the relative proportions of these products.
Researchers at Lehmann's lab are using greenhouse trials to determine which methods of char production have the greatest effect on GHG emissions and soil health.
"Biochar is not just one material," Hyland said, "It's an entire class of materials." Deciding which variety to use will be regionally specific, mainly since readily available feedstocks will vary greatly from site to site.
Hanley said the lab is currently focused on "slow" pyrolysis, which yields a lesser proportion of liquid and gas than higher temperature production methods. Research in Colombia and Guatemala showed that traditional methods of mounding and burying biomass allowed for the production of char without a pyrolysis facility, although such methods cannot capture the heat or syngas by-products.
"Biochar has huge implications for the restoration of degraded lands," Whitman said. But as a solution to climate change, she added, "it is only one of a myriad of options."
It will be a long time before biochar is distributed on a scale large enough to have a significant impact on climate change, Lehmann said. "This is about the long-term. We have to break through the typical research horizon of a decade," he said. In the mean time "the worst thing that can happen is that we have a bunch of happy farmers."