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Biochar: an agri-climatic revolution?

September 2007

Soil, agricultural and climate scientists around the world are currently getting very excited about a very old and until recently forgotten agricultural practice; that of adding charcoal to soil.  Its use is known only in the Amazon, where thousands of years ago the neolithic farmers are thought to of used a technique called ‘slash and smoulder’ where instead of slashing and burning the rainforest, the ‘slash’ was put into piles while still fresh and moist and burnt slowly to produce charcoal.  This was then added to the soil to create what are called Terra Preta do Indio (Amazonian dark earths).  The results of this practice are staggering, even after the elapse of so much time since it was last practiced; Terra Preta soils still have huge stores of carbon and are much more fertile than the same soils that did not receive charcoal.  The modern version of this practice is going under the name of biochar and occasionally the less accurate agrichar. 

The word charcoal is a misnomer; it is not charred coal but charred wood, so it really ought to be called charwood or woodchar.  Biochar is made from any biological material, not just wood, hence the new name ‘charred biological material’ or biochar for short. 

Now the reason the climate scientists are getting excited about this is its ability to prevent the carbon plants have sequestered from the atmosphere from returning there as happens when biological material decays.  The reasoning goes; if the Terra Preta soils have retained their carbon for thousands of years, then putting biochar into soil now could lock that carbon up for an equal time span.  Scientists ‘doing the numbers’ have come up with the startling result that it could even reduce atmospheric carbon dioxide.  As they have pointed out biochar is beyond carbon neutral, it’s carbon negative. 

The news keeps getting better.  The production of biochar produces energy as well as biochar, i.e., it’s also a replacement for fossil fuels burned to produce heat.  If the biochar is produced by pyrolysis, which is where the amount of oxygen, temperature and other conditions of the ‘combustion’ process, are carefully controlled and contained, the volatile fluids and gasses that are lost in standard woodchar production, are trapped and can be turned into more fuel.  This is just stunningly good news for climate change, a process that produces heat, fuel and a material that has the potential to lock up carbon for thousands of years, much more than enough time for us to get over our fossil fuel addiction. 

This still leaves the agricultural scientists jumping for joy.  Not only does biochar have huge potential for climate change mitigation, unlike many techno-industrial processes, which produce synthetic compounds natural systems don't have the capacity to break down and are often toxic, biochar is a natural material, that nature is very familiar with, therefore it should be safe to put into the environment, including the soil.  The fact that doing so has resulted in staggering jumps in crop yield, it’s not surprising farmers and agri-scientists are hopping up and down. 

On the face of it, biochar is almost miraculous, it locks up carbon, produces heat and fuel and produces bumper crop yields, and it can all be done at a local, on-farm scale.  It’s even a great fit with organic principles and philosophy.  What's the catch?  The issue is, despite the hype, articles in the very top scientific journal such as ‘Nature’, the amount of good quality peer reviewed publications supporting the claims are very few indeed, not even hundreds, we are talking handfuls, and no one is looking for potential harmful effects (NB there are a number of papers looking at the Terra Preta in situ, but very few on current agricultural systems).  The old mantra of ‘those than fail to learn from history are condemned to repeat it’ falls on deaf ears when it comes to biochar.  Already an American Senator is trying to rush the technology to market.  However, any technology that has the potential to impact on something as vast as climate change has the potential to have a non-target impact just as big.  As environmentalists and organic devotees, we are increasingly in the position of being unfortunately able to say ‘we told you so’ as the ever increasing litany of harm caused by agricultural and wider practices are ‘found’ by scientists, even ones that a few years ago were considered harmless.  It would be very, very bad news, if after widespread adoption of the technique, with all our soils brimming with biochar that it turned out to have serious negative effects, especially if these affected crop production.  Humanity would then be truly up to its neck in the proverbial.  The organic movement needs to be aware of this potentially revolutionary idea, and while welcoming the possibilities it needs to speak words of caution and not jump onto the bandwagon until it knows the wheels are not going to come off down the road. 


Biochar also adds an interesting angle to the ‘compost debate’ in the last issue.  It has occurred to me since reading Holger’s excellent article and thinking about the comments from other reviews that there may be some confusion over the term humus.  Scientifically humus is biological material that has undergone partial decomposition and is now in a form that is resilient to further decomposition so remains in a pretty stable state, which can last in the soil for tens to hundreds of years.  Unfortunately the scientific definition is not set is stone and varies considerably from one source to the next.  In casual use, humus and (dead) soil organic matter are often used interchangeably, even though the two are quite different.  To measure organic matter soil scientists typically measure total soil carbon, which includes humus, all the dead organic matter and the living ‘organic matter’ i.e., plants and animals, as well.  It is rare for the humus portion of soil to be measured independently of the rest of the organic/carbon fraction, and only in the last decade are scientists routinely measuring the amount of living things and their activity in the soil.  Confusion therefore abounds.

Now, as Holger pointed out, humus has some very important properties such as being a cation exchange site so it’s therefore vial for a health soil.  However, humus production is not the sole provenance of compost.  The addition of fresh plant residues to soil will also result in humus production.  The amounts produced by the different routes may, or, even are likely to, differ, the problem is the research to quantify this, and the effects on soil and plants is not there.  I have finally extracted a copy of Sol (Tim) Morgan’s thesis from the Lincoln University library, who actually did the analysis of the effects of adding the different treatments, and I wish I had it to hand when writing the compost article.  Sol’s conclusions are that the herbal ley treatment had the highest earthworms, higher microbial biomass, higher mineral nitrogen and mineralisable NH4+-N, which were linked to the higher worm and microbial biomass which were in themselves correlated, oh and better water infiltration to boot.  To me that’s a pretty clear result in favour of fresh material.  If you want to read Sol’s thesis for yourself its available in jpg scans at www.merfield.com/sol-morgan/ (warning 14 MB file).  Sol has also said that the best treatment may well be a combination of fresh and composted materials, which Holger also alluded to in his call for balance and timing to which I agree.  Biochar could be the third ingredient on such a list.  The limited research that has been done indicates bio-char to be a kind of super-humus, with a myriad of cation exchange sides and providing save homes for microbes.  I’m therefore going to make the standard utterance of scientists when they get to the end of an article that ‘further research is required’.  To me this just calls out for a long term trial, like the one Bob Crowder set up in the apple orchard, to compare the use of fresh vegetation with the same fresh vegetation composted and made into biochar plus mixtures of the three and study the effects of the materials on the soil and crops grown in them.  This could give us some fascinating insights into the very foundation of organics; a healthy soil. 

A JPEG version of the thesis of Timothy (Sol) Morgan who conducted the research on Bob Crowders apple orchard trial is avalible here (14 MB zip file)

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Copyright 2008 Charles N. Merfield.