Whatever happened to biochar?

From http://www.biocharretort.com

I have been reading 'Ten Technologies to Fix the Planet' by Chris Goodall which is a little bit out of date now (it was published in 2008) so it is interesting to see how the technologies he recommended are faring. The one which seems to be going absolutely nowhere is biochar – capturing carbon by heat treating biomass and mixing it into soil. Carbon created this way can stay in the soil for centuries and improves fertility in a number of ways, not least by improving its water holding properties and drought tolerance.

Chris says: ‘..making charcoal is easy and can be done profitably by poor farmers in the tropics,’ and he reports on a trial in Cameroon where subsistence farmers added biochar to corn plots and significantly increased yields, up to double the normal.

Soils hold enormous quantities of carbon: 1600 billion tonnes globally, according to Goodall which is twice that in plants and trees and 200 times as much as we generate from fossil fuels each year. We could add a great deal of carbon to the soil without making much overall difference to the carbon cycle. Also biochar can be made very cheaply. So – how come we still can’t invest in biochar for carbon offsetting as I suggested in my post last year Carbon offsetting - does it really work?


I am coming round to the idea that biochar, though it has huge potential benefits, also carries serious risks and in practice it may be impossible to manage. Australia seems to be closest to having a standard for using biochar and it is still some way off. Although its new Carbon Farming Initiative explicitly lists biochar as a potential activity for carbon storage it does not have an approved methodology for assessing projects using it, nor even one under consideration.

What is Biochar?

Biochar is more or less the same thing as charcoal except it is used in agriculture rather than being burnt for energy. Since biochar is supposed to remain in the soil for a long time, you need to be a bit more careful of what is in it than if you are just going to burn it.

• You don’t want any contamination with heavy metals or other toxins.
• You want to make sure that the carbon is properly stabilised.
• For good water holding properties you need the right particle size and structure (which means you need a higher temperature to make it than ordinary charcoal).
• Biochar can be strongly alkaline, which is great for neutralising acid soils but if yours isn’t then you need to be careful.
• Biochar can contain nitrogen and other nutrients which it is useful to know about.

If you are a poor farmer you don’t want to have to measure these properties but you don’t need to. Most of them are directly related to what you make the biochar from and how you make it which you can control, more or less, depending on your equipment.

Biochar for carbon storage

If you want to invest in biochar as a carbon storage mechanism, you also need to be very careful also about what biochar is made from, how it is made and how it is used.

• It must be made from waste material or from biomass products which have been grown sustainably. Chopping down the virgin forest to make biochar will increase carbon in the atmosphere, not reduce it.
• It must be made using a clean efficient process which locks up the carbon in a stable form and doesn’t release greenhouse gases during the process. As I described in How Green is my Charcoal Barbecue?, heating the material to make char inevitably produces some methane which is a very powerful greenhouse gas – 70 times more powerful than CO2 in the short term. It is essential this gas is captured and used, or at least flared off. However, traditional charcoal making techniques don’t control the gases coming off.
• Biochar needs to be mixed properly into the soil. If it just sits on the top it will either dry out and blow away or be washed away in a heavy rain. Tiny carbon particles in the air are a health hazard and will increase global warming rather than reducing it.

All these considerations and a few more are included in the current European Biochar Certificate standard published by the Biochar Science Network.

A recent paper in Brazilian Agricultural Research [1] points out that the oversight needed to prevent abuse of financial incentives is similar to that needed for sustainable forestry and says ‘although debate over the relative merit of each forestry certification scheme continues, it appears that in those countries that undertake international sustainability reporting … and have adequate governance to ensure compliance,…there is evidence that there are improved sustainability outcomes. Where there is no reporting obligation, or absence of mechanisms to ensure measurement, monitoring or compliance, the reverse is true.’

Biochar could pay for itself as a soil fertility treatment on a local scale, but local production methods are unlikely to meet all the requirements for sustainable carbon storage. You can do it at home, - this video shows how to make it in small batches or you can buy efficient retorts such as that pictured above from http://www.biocharretort.com - and then it is up to you to make sure you are reducing climate change and not increasing it.

It looks like large scale use of biochar for carbon storage is likely to cost more in bureaucracy than in technology – if it ever does get off the ground.

[1]  Annette L. Cowie, Adriana E. Downie. Brendan H. George, Bhupinder‐Pal Singe, Lukas Van Zwieten and Deborah O’Connell (2012) Is sustainability certification for biochar the answer to environmental risks? Pesq. agropec. bras., Brasília 47(5)