Biochar is made by burning organic matter anaerobically, i.e. in the absense of oxygen - a process known as 'pyrolysis'. Biochar has been used as a soil conditioner for centuries by Amazonian indians - the terra preta soils that they created have persisted for at least 7,000 years. Current interest in its use has focussed on a number of its advantages for both agriculture and mitigation of climate change.
The large surface area of biochar particles creates a ‘reef’ system in the soil which encourages the growth of mycorrhizial fungi, a fungi which lives symbiotically with plants and encourages plant growth as well as being the base of the food web for beneficial soil fauna such as collembola. In addition, biochar improves soil structure, breaks down pesticides, suppresses methane emissions and acts as a long term carbon store which mitigates CO2 build up in the atmosphere. Hence, by using biochar for soil improvement, you are promoting climate smart agricultural practices.
Biochar can contribute 15 to 50% of the carbon reduction needed by 2050, making biochar as important as CO2 capture and geological storage, renewable energy and nuclear energy.