Saw a show the other night talking about the Amazon soils and how they are now excavating and seeing just how much charcoal was added into the soil compared to nearby areas where no charcoal was added. It was amazing!!! Here is another link that gives some good info on Terre Preta that even I could understand... Neat topic!!!
BioEnergy Lists: Terra Preta (Biochar) | Information on the intentional use of Biochar (charcoal) to improve soils.