Excerpt -- full article here:
"In field trials with corn, rice and many other crops, biochar has increased productivity by making nutrients already present in the soil better available to plants. Results are especially dramatic when biochar is added to good soil that contains ample minerals and plant nutrients. Research continues (track it at The International Biochar Initiative), but at this point it appears that biochar gives both organic matter and microorganisms in organically enriched soil enhanced staying power. Digging in nuggets of biochar ? or adding them to compost as it is set aside to cure ? can slow the leaching away of nutrients and help organically enriched soil retain nutrients for decades rather than for a couple of seasons."
Charlie