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Biochar for carbon sequestration

Tony Callaghan 23/12/2021

Biochar for carbon sequestration

Biochar - sequestration diagram, C Steiner, 2008

Biochar to Tackle Climate Change

Biochar has an enormous potential to help mitigate climate change by locking (sequestering) the carbon into the soil. The detailed numbers can be overwhelming so just one headline: biochar has the potential to offset up to 12% of the TOTAL CO2 emissions. 

(If you want more detail, a good read would be Dominic Woolf's summary in Nature Communications).

12% might not sound huge - but when it is linked with the fact the technology (pyrolysis) is well understood and ready to implement at scale plus the science around the benefits of adding it to soil are well known, then biochar enters a 'small and significant' group of negative carbon options available as we head toward 2030 and the net-zero goal.  

Here at SoilFixer, we have been preparing for take-off for some time. All the pieces of the jigsaw are now aligned.  We aim to make 2,000 tonnes per annum in our pilot project. The plan is to grow this via multiple sites to  300,000 tpa - offsetting 1 million tonnes of carbon dioxide (7% of the UKs net-zero target). Join us and help make it happen. 

1Kg of biochar carbon offsets approx. 3 Kg CO2e (see calculation below)*

Every gardener,  farmer and landowner can help offset (mitigate) climate change by adding biochar or biochar super compost (SF60) to their soil. Every government and corporate entity can help support the industry by purchasing biochar offset credits. 

In this blog, we explore how biochar is used to mitigate climate change. The role of biochar in terms of soil carbon, compost, humus, and soil organic matter.

The world has declared a climate emergency.’  There are lots of changes we can (and will have to make) to reduce our personal carbon footprint - growing some fruit and vegetables, composting, using fewer chemicals and plastic, the list goes on. Here at SoilFixer we talk about the benefits of making your own compost a lot and how adding colloidal humus and biochar can help enrich it, biochar not only provided a multitude of benefits for plants, it also plays an important role in reducing carbon by simply adding it to the soil.

There is ongoing research and development that is looking at all sorts of sequestration options and soil is one option. If we add 1Kg of soil carbon we offset approx 3 Kg CO2e (see calculation below). All the earth’s soils have the ability to store more carbon. Estimates range from the ability to offset 10-20% of all global emissions – that is potentially a huge dent in the target.

Naturally occurring soil carbon

Soil Scientists use the terms Soil Organic Matter (SOM) and Soil Carbon (roughly 50% of the total SOM figure). These terms include all organic-Carbon. For locking up carbon in soil (i.e. mitigating climate change), only those forms of Soil carbon that are resistant to biodegradation are helpful. Only a tiny amount of the plant organic matter that enters the soils forms into recalcitrant, resistant to decay carbon. This fraction is usually termed the humic fraction. (Note humus to soil scientists does not mean well-matured compost!) 

Storing carbon in soil already happens, it is a natural process, it does not need and new technology, it just needs everyone and every farmer to understand that it is a viable option because every time we dig over our gardens we reduce the number of nutrients stored in the soil and carbon dioxide is released into the atmosphere; this happens on a huge scale in farming and agriculture. There are a few changes that can be made to prevent SOM/Soil Carbon decline such as considering using the no-dig  / no-till method, making your own compost, and adding it to the soil regularly.

Compost and soil carbon

Compost is biodegradable. Only a tiny fraction (estimated at <1%) forms into long-term soil carbon. (take-away tip: adding lots of compost to your soil will NOT increase your soil-carbon. It is estimated that it would take 20-50 years to re-build soil using compost and organic matter). Unfortunately, this fact led soil carbon sequestration not being on the early lists of the Intergovernmental Panel on Climate Change (IPCC) lists of urgent technologies to investigate. Thanks to the hard work from various biochar organisations such as the IBI and EBC this situation has been updated and biochar is now on the list.

Biochar and Soil Carbon

Biochar is non-biodegradable so it has the ability to remain in the soil for hundreds, if not thousands of years. It can also play a huge role in reducing our carbon footprints: every 1kg of biochar can offset 1Kg of carbon, i.e. 3.6Kg of carbon dioxide. Why isn’t everyone covering their gardens with it and farmers using it on their fields? It is expensive to produce and therefore expensive to buy (in large quantities). The solution to this is to do a little bit every year to lessen the financial strain, not will your soil be healthier but plants and edibles will benefit too whilst you help reduce climate change.

For those looking for a really in-depth review of biochar versus other off-setting technology, we recommend reading the European Biochar Initiative white paper via this link

The biochar industry has been advocating that increasing soil carbon can be achieved in 1 year via biochar….

* Please note: the actual offset for each biochar will depend on the % carbon content. Our biochar is 85% carbon. Some biochars can be as low as 60%, some as high as 95%. We then have to consider "permanence" - how long does the biochar stay in the soil. After a long discussion period, the biochar organization (EBC, IBI) has agreed with IPCC that the hydrogen to organic carbon ratio (H/Corg) will be used to determine the volume of carbon at 100 years. A considerable safety buffer has been built into the calculation, and again the H/C will vary by vendor. Our biochar comes out at 85% retention at 100 years.    If you wanted to formally claim Offsets (sequestration) funds, the accurate calculation would be 3.67Kg*0.85 (%C) *0.85 (100 yr H/C) = 2.65 Kg CO2e offset).

Biochar Super Compost (SF60) and Soil Carbon

Although it is still early days around testing and evidence… SF60 (our mix of compost (40%), biochar (20%) and colloidal humus (40%) is looking promising as a new type of sequestration technology. The colloidal humus appears to be resistant to biodegradation (in our tests > 50 years). By increasing the amount of colloidal humus from 1% in compost to 40% in SF60, we increase the amount of carbon in soil. Those quick on the maths will spot that biochar has just become a lot more cost-effective. (We achieve 60% of the impact using 20% of the cost. (0.2/0.6 = 0.33, i.e. x3 more cost-effective).

Where does our compost activator (humification agent) fit in?

If you are home composting – then add the humification agent to your compost. Not only will you add biochar, but you will also make colloidal humus. Both offset your carbon footprint and the compost you get is a great organic, natural soil improver that will increase yield and flowers (20% more) as well as support plant health and resistance to drought.

  • 1 Kg SF60 has the potential to offset 1Kg CO2e (figures updated 18/09/20)*

(* Our tests indicate this, but we recognise the tests have yet to be validated by an external independent body).

You can buy our Humification Agent, Biochar and SF60 Super Compost from our online store here.

Tags: biochar, climate change, soil