Biochar is a stable carbon rich solid made by heating biomass with very little oxygen, a process called pyrolysis. The carbon in it resists decomposition for a very long time, so adding it to soil holds carbon out of the atmosphere while also improving the soil ability to retain water and nutrients.
The process
Burn biomass in open air and it combines with oxygen, releasing heat and returning its carbon to the atmosphere as carbon dioxide. Heat that same biomass in an environment with very little oxygen and something different happens. It cannot fully combust. Volatile compounds are driven off as gas and oil, and what remains is a porous, black, carbon rich solid.
That process is pyrolysis and the solid is biochar. Humans have made charcoal this way for thousands of years. What changed recently is the reason for making it: not to burn it, but to bury it.
Why the carbon stays put
Plant material left on the ground decomposes. Microorganisms break down its carbon compounds and most of that carbon returns to the atmosphere within a few years. This is the normal, fast carbon cycle, and it is why leaving crop residue in a field does not constitute carbon storage.
Pyrolysis changes the chemistry. The carbon in biochar is rearranged into structures that soil microorganisms find very difficult to break down. The material becomes chemically resistant in a way the original biomass was not. Put it in soil and a large fraction of its carbon remains there far longer than the plant it came from would have lasted.
How much longer depends on how the char was made. Pyrolysis temperature and duration change the structure of the resulting material, which is why process conditions are recorded per batch rather than assumed. A char made carelessly is a much weaker claim than a char made under controlled and documented conditions.
Why carbon buyers pay a premium for it
Carbon removal buyers have become preoccupied with a single question: can this be undone.
A growing forest genuinely removes carbon from the atmosphere, and it holds that carbon only for as long as it stands. It can burn. It can be cut. It can die in a drought. The carbon accounting for forestry has to account for that possibility, and the market has learned the hard way that it often did not.
Biochar sits at the other end of that spectrum. Once the char is in the soil, there is no straightforward mechanism by which its carbon returns to the atmosphere. That durability is why buyers holding themselves to strict standards, including several of the large technology companies buying removal at scale, have concentrated their purchasing on durable forms rather than on forest credits.
Why this fits land restoration particularly well
For a company restoring degraded land, biochar resolves a problem that otherwise has no good answer.
Restoration produces residue. Pruning, thinning, crop stalks, woody material that has to go somewhere. Selling it as biomass fuel requires a buyer within an economic haulage distance, and on remote or arid land there frequently is not one. Burning it in the field wastes it and returns the carbon immediately.
Pyrolysing it on site converts a transport problem into a storable, valuable product. And the by product goes back into exactly the soil that needed it, because the ground being restored is by definition low in organic matter and poor at holding water, which is precisely what biochar helps with.
So a single operation produces a saleable carbon removal product and improves the asset it was produced on. That is unusual, and it is why we treat pyrolysis as part of the land work rather than as a separate business.
What determines whether a batch is any good
Four things, all of which are recorded rather than estimated.
Feedstock. What went in determines what comes out. Clean woody residue behaves differently from mixed agricultural waste, and contaminated feedstock produces char that should not go into soil at all.
Temperature and residence time. These shape the structure of the carbon and therefore its stability. They are the main process variables and they are recorded per batch.
Mass in and mass out. A carbon claim requires knowing how much feedstock entered and how much char resulted. Without both numbers there is no defensible figure.
What happened to the gas. Pyrolysis releases volatile gases. Whether those are captured and used as process heat or simply released changes the overall emissions picture of the operation, and an honest accounting includes it.
A biochar carbon claim that does not carry these four is not a claim, it is an assertion. Our measurement approach records them per batch for the same reason we record survival counts per plot: a number nobody can check is worth nothing to a serious buyer.
Related questions
- How is biochar different from ordinary charcoal?
- They are made by the same process. The difference is purpose and control. Charcoal is produced to be burned as fuel, so its carbon returns to the atmosphere. Biochar is produced under controlled conditions to be added to soil, where the carbon stays put, and the process conditions are recorded because they determine how stable it will be.
- Why do carbon buyers prefer biochar to tree planting?
- Because of permanence. A forest holds carbon only while it stands, and it can burn, be cut or die, releasing that carbon again. Biochar carbon is chemically resistant to decomposition once it is in soil, so it is far less exposed to reversal. Buyers with strict standards pay more for removal that cannot easily be undone.
- Does biochar improve soil?
- It improves the physical behaviour of soil rather than acting as a fertiliser. Its porous structure helps soil hold water and retain nutrients that would otherwise wash out, and it provides habitat for soil microorganisms. On degraded, low organic matter soil these effects matter more than on already fertile ground.