The carbon stability of biochar and the effects of biochar on other soil carbon sources is highly dependent on biochar properties and use systems.
Biochar is a carbon-rich soil additive made by heating biomass in a low-oxygen environment - a process called pyrolysis. Pyrolysis chemically transforms the carbon in biomass, which forms stable ring structures that are resistant to decomposition and decay. Controlled, high-temperature pyrolysis can improve the stability of biochar carbon, resulting in high quality biochars which are more effective at locking up carbon.
This means that when biochar is added to soil it can remain stable for hundreds to thousands of years. This permanence in the soil is not sensitive to farm management practices. Unlike other methods to increase soil organic carbon, such as green manures, biochar carbon does not require any maintenance or long-term changes to soil management.
Biochar can also improve other pools of soil organic carbon by slowing the decomposition of other organic matter in the soil, in a process known as negative priming. When applied with organic fertiliser, our field trial results show that total organic carbon in slurry can increase by up to 43%, even with a low biochar application rate of 5%. When co-applied with other carbon sources such as manure, low-dose applications of our biochar at a rate of just 1 ton per hectare can increase total soil organic carbon by up to 2%.
The biochar production process (pyrolysis) creates chemically stable carbon in biochar. This carbon can be stored in soil for hundreds of years, increasing soil carbon.
Our biochar can slow the decomposition of newly incorporated organic matter, such as carbon in organic fertilisers, enhancing soil carbon. This process is called negative priming.
Biochar carbon storage can be certified using existing methods at the point of production and requires no on-farm sampling. Some certification examples include the European Biochar Certificate, and the International Biochar Initiative.