biochar

:  a form of charcoal that is produced by exposing organic waste matter (such as wood chips, crop residue, or manure) to heat in a low-oxygen environment and that is used especially as a soil amendment … the US could convert huge amounts of logging and agricultural leftovers into biochar, and even grow crops just for that purpose. — Josh Harkinson, Mother Jones, November/December 2008 … biochar holds such promise as an inexpensive and highly effective way to sequester carbon in soil. — Al Gore, Our Choice: A Plan to Solve the Climate Crisis, 2009