What is biochar?
‘Biochar’ is a catch-all term describing any organic material that has been carbonised under high temperatures (300-1000°C), in the presence of little, or no oxygen. This process (called ‘pyrolysis’) releases bio-oils plus gases and leaves a solid residue of at least 80% elemental carbon which is termed biochar.
Virtually any organic material can be pyrolysed to make biochar. Different biochar feedstocks result in biochar with different properties, which is why it is important to know what material your biochar has been made from. Examples include soft plant tissue, woody materials, and manures. The property all of these biochars share is that they are carbon rich and don’t readily decompose.
The idea of using biochar in soils was born from observing the man-made ‘Terra Preta’ soils of the Amazon. The fertility of the poor, acid soils in this region is thought to have been improved through addition of charred organic material by the area’s indigenous inhabitants: helping to sustain population expansion across the Amazon region.
Biochar retains much of the open capillary structure from the original wood, including xylem vessels. In soil these channels continue to function as conduits for air, water, nutrients and biology.