Alex Steffen of Worldchanging says,
My colleague Jer Faludi has written up the best overview I've yet read about how biochar/gasification systems work. Given that there is at least the theoretical potential here to create a carbon-negative energy source (that is, an energy source that over the course of normal operation actually *removes* carbon dioxide from the atmosphere), the char/gas combo has a lot of people, um, fired up.
(Though it's important to remember that when dealing with complex systems like climate, topsoil and farm subsidies, no bullet is as silver as it looks from afar.)
"We've mentioned terra preta before: it's a human-made soil or fertilizer. "Three times richer in nitrogen and phosphorous, and twenty times the carbon of normal soils, terra preta is the legacy of ancient Amazonians who predate Western civilization." Although we don't know how it was made back then, we do know how to make it now: burn biomass (preferably agricultural waste) in a special way that pyrolisizes it, breaking down long hydrocarbon chains like cellulose into shorter, simpler molecules. These simpler molecules are more easily broken down by microbes and plants as food, and bond more easily with key nutrients like nitrogen and phosphorus. This is what makes terra preta such good fertilizer. Because terra preta locks so much carbon in the soil, it's also a form of carbon sequestration that doesn't involve bizarre heroics like pumping CO2 down old mine shafts."