Biochar is essentially charcoal made under carefully controlled conditions. By burning carbon-rich compounds in the absence of air (pyrolysis), the volatile and non-carbon components are burnt off, leaving much of the carbon behind as a solid ‘char’.
This has particular properties that make it valuable as a means of storing carbon, especially in the soil. It has been found in stable condition after thousands of years, making biochar a potentially useful tool in carbon sequestration and storage.
Biochar can be made from any readily available carbon source, e.g. wood and agricultural residues such as rice husks, nut shells and beet tops, and the quality of this source material (feedstock) partly determines the properties of the biochar. For example, if the feedstock is nutrient-rich, so will be the char. By-products of pyrolysis include a biogas and a tar, both of which have useful applications.
This description of Biochar comes from The Centre for Alternative Technology's Zero Carbon Britain Report Section 3.6.3 Capturing carbon. See their report for the full details and references.
There are two events on Biochar coming up in the region. select on the image below for more details.