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Biochar is a carbon-rich material created from the controlled burning of organic matter. The material is baked so that all the volatiles are off-gassed and burnt and air restricted so that the carbon is not burnt.


It is a powerful soil amendment that helps to improve soil health and fertility, increase water retention, and reduce soil acidity. Biochar is an excellent addition to any garden or agricultural project, and can help to boost plant growth and yield.


Biochar also has the potential to sequester carbon in the soil for centuries, helping to reduce carbon dioxide in the atmosphere.

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What's so good about biochar?

Nano tubes in the biochar:

  • act like a sponge (for water & nutrients)

  • provide homes for bacteria and fungi

  • have a massive amount of surface area

This means that biochar improves sandy soil (holds more water) or clay soil (holds more air). 

Biochar degrades very slowly in the soil, hundreds to thousands of years, and so is a great way to sequester carbon out of the air.

Glossary of biochar related terms 

feedstock – biomass which is pyrolised to turn into biochar.

syngas or wood gas – a mixture of primarily hydrogen, carbon monoxide, and methane which is driven off during pyrolysis.

bio-oil – condensed liquid hydrocarbons which are driven off during pyrolysis and can be used in blending biodiesel and other fuels.

wood vinegar – a liquid complex of acetic acid, acetone and methanol along with organic compounds, and familiar to anyone who has watched sap bubbling from the end of a log as it burns. Used commercially as a flavouring ingredient (liquid smoke).

pyrogenic carbon – carbon formed in the presence of fire, such as charcoal, which is effectively removed from the biological carbon cycle for an extended time. On a global scale, pyrogenic carbon accounts for an average of 13.7% of soil carbon stocks.

pyrolysis – the process of heating material in a low-oxygen environment. This can be accomplished in a retort, which vents the evolved gases but does not admit air for complete combustion, or by the design of the burn chamber to limit airflow into the zone of high heat.

graphene – a crystalline form of molecular carbon comprising layers of atoms arranged in hexagonal rings by aromatic bonding. Graphene is interesting because its structure provides the highest availability among all forms of carbon of edge atoms for chemical reactions. Pyrolysis of biomass at appropriate temperatures promotes the formation of this type of structure as the volatile fractions are driven off and the weaker aliphatic bonds in the chain-like molecules are broken down.

flame cap – a zone of active flames across the top of a bed of coals which serves multiple purposes: to consume the evolved gases and provide full combustion to minimise smoke and particulate exhaust, and to deprive the coals of oxygen and prevent combustion of the carbon.

exothermic – a reaction or process that gives off more heat than is applied.

cation exchange capacity (CEC) – the ability of a substance to attract and hold positively charged ions in solution.

terra preta – Portuguese for “dark earth” and the term used to describe the anomalous zones of fertile soils found in the Amazon basin where indigenous people had systematically added charred wood, bone, manure, and food waste to their soils in order to farm the same land continuously.

Note: This glossary originates from SlowFarm and has been gifted by Phil Stevens.

Further reading

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New Zealand - Biochar Network New Zealand (BNNZ)

Australia - ANZ Biochar Industry Group (ANZBIG)

USA - US Biochar Initiative (USBI)

        - USDA Forestry Service biochar page

        - Wilson Biochar resources

        - Dr TLUD biochar-making wood-stoves

International - International Biochar Initiative (IBI)

Europe - European Biochar Certificate (EBC)

            - the Biochar Journal

            - Nordic Biochar Network (NBN)

            - research group at the Swedish University of Agricultural Sciences (Biochar Systems)

            - learnings from the Stockholm Biochar project (shared on Stockholm Tree Pits)

This Biochar resource created by Passionate Permie Dylan - July 2023

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