Such an approach could carry an extra benefit. Burying char–known as black-carbon sequestration–enhances soils, helping future crops and trees grow even faster, thus absorbing more carbon dioxide in the future. Researchers believe that the char, an inert and highly porous material, plays a key role in helping soil retain water and nutrients, and in sustaining microorganisms that maintain soil fertility.
This MIT Technology Review article is interesting. Carbon-neutral biomass burning is a common proposal to offset hydrocarbon fuel burning. But the pyrolysis char-squestration strategy results in net carbon reduction — if there is an economic basis for farmers et al to both fund the process and give up the energy they would have obtained by burning the biomass.
Lehmann estimates that as much as 9.5 billion tons of carbon–more than currently emitted globally through the burning of fossil fuels–could be sequestered annually by the end of this century through the sequestration of char. “Bioenergy through pyrolysis in combination with biochar sequestration is a technology to obtain energy and improve the environment in multiple ways at the same time,” writes Lehmann in a research paper to be published soon in Frontiers in Ecology and the Environment.
…Fowles believes that storing black carbon in soil carries less risk, would be quicker to implement, and could be done at much lower cost than burying carbon dioxide in old oil fields or aquifers. And he says the secondary benefits to agriculture could be substantial: “Biochar reduces the soil’s requirement for irrigation and fertilizer, both of which emit carbon.” Fowles adds that it has also been shown to reduce emissions of greenhouse gases from decay processes in soil. This would include nitrous oxide, a potent greenhouse gas. “Biochar has been observed to reduce nitrous-oxide emissions from cultivated soil by 40 percent.”
David Layzell, an expert on bioenergy and plant sciences at Queen’s University, in Kingston, Ontario, says that finding the right balance between energy generation from biomass and sequestration of its char is a major area of research with global implications. “The issue of how much you should burn and how much should go back to the land is partly an economic issue and partly a sustainability issue. We don’t have the full answers to this, but that’s the kind of research we need.”
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