From earth to earth: biochar promises to act as a fuel improver and sequester carbon in the soil, but the actual benefits have yet to be fully quantified.(Food & agriculture)

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Biochar is charcoal added to the earth as a soil conditioner to improve crop yields. It is a carbon-rich material made by heating plant material in the absence or near absence of oxygen; the organic matter is degraded by heat, but not combusted, and aromatic carbons are produced. These carbons are difficult for microbes to break down and so the carbon in biochar is not simply recycled back into the atmosphere as it would be in other organic matter. Bury this biochar in soils and billions of tonnes of carbon may be sequestered annually, proponents say, reducing greenhouse gas emissions. It also improves plant growth: a win-win scenario.

Biochar advocates, especially the International Biochar Initiative, want biochar included in any new agreement that replaces the Kyoto Protocol, so that it can earn carbon credits under the Clean Development Mechanism (CDM).

Deciding how much biochar improves plant growth in soil and reduces carbon emissions through the entire system is critical to such calculations; char may improve plant growth and thereby reduce the need for fertiliser, delivering a carbon saving because fertiliser manufacturer is energy hungry. The logic: reduce fertiliser usage, save energy, emit less carbon dioxide. Also, rotting biomass gives off methane, a potent greenhouse gas, so rather than let plant material decay, pyrolysing it and burying it as biochar reduces methane emissions. It may also reduce nitrous oxide emissions, another greenhouse gas. But quantifying all these emission reductions is a work in progress, and research has only really begun. …