Terra Preta is an ancient Amazonian agricultural technique that restores soil fertility, sequesters carbon and provides carbon-neutral or even carbon-negative energy. This ‘emerging’ technology for the treatment of wood waste involves slowly burning unwanted organic matter and adding the charred remains (‘biochar’) back into the soil. Not only does the technology sequester carbon but making biochar releases heat, meaning that biochar production can also constitute a fuel source. Cornell University is testing the technology by heating a poultry house using poultry litter.
Biochar is made by combustion of biomass in a low oxygen environment. These conditions can be found in several processes including fast pyrolysis75, slow pyrolysis76 and gasification.77 A New Zealand company is making biochar using industrial microwave technology (see 4.3.9). Biochar quality is affected by the type source material (wood, food or municipal waste for example), and processing conditions such as temperature and time. There are indications that biochar provides some agricultural benefit when injected in the soil but this varies depending on its quality as well as other variables such as soil type, climate and crop type.78
Australian company Crucible Carbon has partnered with the Western Australia Agriculture Department in a project to convert agricultural residues and woody crops into biochar and renewable energy. Application of biochar to wheat crops is reportedly already demonstrating agricultural benefits.79