Biochar is "organic matter that is carbonised by heating in an oxygen-limited environment, and used as a soil amendment" (IPCC).
A wide range of organic matter can be used to produce biochar, as long as it is renewable. At NetZero, we use agricultural residues which would have otherwise be left to rot or burnt. For example: coffee or cocoa husks and shells; coconut shells and fibers; peanut or cashew shells; palm empty bunches; etc.
Biochar's production process is based on pyrolysis, a thermochemical reaction where intense heating in the absence of oxygen breaks down complex molecular chains and rearranges molecular bonds to form a very stable product.
The global sustainable potential for negative emissions through biochar is between 1 and 2 GtCO2 per year.
Biochar's main chemical component is carbon. This carbon was originally captured by plants in the atmosphere during photosythesis, and was then extracted and stabilised during the pyrolysis process. If put in the soil, this carbon remains there for at least hundreds of years. Thus, biochar is a long-term carbon removal solution.
The IPCC reports that, when deployed at a global scale and taking into account sustainability constraints, biochar could remove every year up to 2 billion tonnes of CO2 from the atmosphere. This could be a significant contribution in tackling the hard-to-abate emissions, which are estimated to be 10–15 billion tonnes of CO2 in 2050.
Biochar is used in agriculture as a soil amendement, to be mixed with topsoil and applied only once.
The physicochemical properties of biochar allow to improve soil's quality: its high porosity improves the water-holding capacity of soils; its negatively charged surface allows for better nutrient retention; and its high carbon content helps rebalance acidic soils. The result is a durably improved crop productivity and the possibility to switch to 100% organic farming.
Biochar in agriculture is most effective on tropical crops. Jeffery et al. (2017) has shown a global average production increase of +25% in the tropics at a median biochar application rate of 1.5 kg/m2.
At NetZero, we provide agricultural training and support to farmers to use the biochar, with the support of Earthworm Foundation.