The charcoal used for soil ammendment & carbon sequestration is definitely NOT equatable at all with volcanic "ash", nor the charcoal byproducts of fire. Read my original post. Charcoal is produced by heating organic material, mostly some form of cellulose, in a closed vessel in the absence of oxygen. The scientist I heard speak was talking about pure carbon charcoal, not burned or otherwise processed. Minerals and water are absorbed by carbon in this form (ever hear of charcoal filters?) and plant roots retrieve them. The idea is to convert organic material to charcoal because it is a "green" process (sequesters more CO2 than it produces, and if done using reflective solar vessels, consumes no other energy) and it effectively sequesters the carbon for tens of thousands of years if tilled into the soil. It also does not tie-up oxygen, which was Patrick's original question. Too, solid carbon in the form of charcoal is much denser that gaseous carbon (carbon dioxide, carbon monoxide), therefore is in a much more efficient form for sequestration in terms of volume. It works regardless of soil temperature or location. And by enriching the soil, it becomes more productive, which in turn produces a greater living carbon sink of crops and other plants.