'''Biochar''' is a name for charcoal when it is used for particular purposes, especially as a soil amendment.
=== Overview ===
Some of the world's most productive soils (e.g. Canadian prairies, Russian [http://en.wikipedia.org/wiki/Chernozem Chernozem] / or "black earth") are very rich in organic carbon. This is now thought to be pyrogenic in origin, likely originating from prairie or forest fires. This carbon is often thousands of years old, demonstrating its stability in soil. For more extensive background on Biochar, please consult the [http://en.wikipedia.org/wiki/Biochar Wikipedia entry on biochar].
=== Production ===
The pyrolysis temperature appears to be a critical factor determining char yield vs. energy yield (tradeoff). Flexi-pyrolysis units are being developed that can be set for either char yield or gasification yield. Dry biomass can be pyrolyzed at regular atmospheric pressure. For wet biomass, pyrolysis at higher pressure ("supercritical") may be necessary, requiring a more sophisticated technical set-up.
When large chunks of wood are used as feedstock, the charcoal may need to be crushed before use (beware: coal dust explosion !). Many agrigultural feedstocks and leaf litter will not need to be pulverized but will readily break into smaller pieces by themselves. For information on small-scale gardening, please consult the [http://biochar.pbwiki.com/ Gardening with Biochar FAQ], an excellent resource.
===Biochar as a method of carbon sequestration===
== Terra preta ==
'''Terra preta''' is a type of very dark, fertile anthropogenic soil found in the Amazon Basin. It is basically a mixture of charcoal, bone, and manure. It is very stable and remains in the soil for thousands of years.