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One way to sequester carbon in your own backyard (or container garden) is by using biochar. Biochar is essentially charcoal, but instead of being used as a fuel, biochar is used to support life in the soil. As a soil amendment, biochar can add to plant productivity and health, while also locking away carbon for centuries underground.
Finding a local producer is ideal, but you can also find biochar in stores. It’s also possible to make biochar yourself.
Once you have some, you might add it to your compost bin. This is called co-composting, and it just might be the best way to prepare it. Biochar aids the composting process in part by absorbing nitrogen, which might otherwise be outgassed as ammonia (smelly) and nitrous oxide (a greenhouse gas). Biochar also acts as a home for microbes and a sponge for water, much like it does in the soil, which can accelerate the composting process. Some studies have found this to be beneficial to plant growth in ways that can’t be replicated by combining biochar with finished compost.
Biochar can also be combined with compost, manure or mineral dust, etc. before application. Some biochar products may come premixed with a source of nitrogen and other key plant nutrients. While a nutritionally-balanced approach is probably ideal, most of the science on biochar in agriculture to date has been conducted with relatively heavy applications of pure biochar, in part because the experimental variables are easier to control. Those studies have shown a number of benefits from biochar alone:
Increased…
- Plant productivity
- Crop yield
- Photosynthetic rate
- Water use efficiency
- Plant-available soil water
- Root biomass
- Root length
- Number of root nodules
- Soil microbial biomass
- Soil organic carbon
- Available phosphorus
And decreased…
- N2O emissions
- Toxic metals in plants
Not only is the biochar itself a stable form of carbon, but it decreases N2O emissions from the soil, and leads to a further increase in soil organic carbon. Plus, it can lead to greater above-ground biomass and reduced water usage. All of this helps to combat climate change.
The biochar itself is stable for so long in the soil because it is primarily inorganic carbon (without hydrogen). Biochar is produced through pyrolysis; that is, heating in the absence of oxygen. The feedstock (typically wood or crop residue) does not burn, but rather produces a gas consisting mainly of N2, CO and H2, and a bit of CO2, CH4 and O2. This gas is flammable, and is used to produce more heat, which keeps the pyrolysis process going and hopefully produces mainly N2, CO2 and water vapor. Pyrolysis causes the hydrocarbons in the feedstock to lose their hydrogen, as well as oxygen and nitrogen, leaving pure carbon rings and chains, preserving much of the microscopic structure of the original organisms. This structure and the electrochemical properties of carbon allow biochar to act as a reservoir and conduit for both water and electric charge in the soil.
More on where to get biochar
Biochar is produced in massive industrial stoves, in big box kins, ring kilns, kon-tiki kilns, rocket stoves, retorts, or just in a simple hole in the ground. If you’d like to try making biochar, please consult your local authorities regarding permitted burning and fire safety. Quench your biochar and store it wet to avoid risk of fire.
If you’d like to purchase biochar, check your local garden supply store for ready to use biochar mixes for compost or soil conditioning.
$30 for 8 quarts at time of publishing
Rosy Soil
If you can’t find a local option, check out this mix available online. Rosy Soil sells indoor potting mixes that use biochar and best of all, are peat-free.
More resources
Application rate calculator
This tool, developed by our project partner Pacific Biochar allows you to calculate how much biochar is needed to achieve the desired increase in % organic matter for a specific project, like composting or landscaping.
Try application rate calculator
U.S. Biochar Initiative
A not-for-profit organization promoting the sustainable production and use of biochar through research, policy, technology and implementation. USBI publishes quite a few educational articles on applications of biochar. If you have specific questions or would like to volunteer, contact John (john@biochar-us.org).