Biochar—or charred biomass intended for use in soil—is a much talked about topic in permaculture and organic gardening. There's been a lot of hype on this topic, suggesting that it can massively increase soil carbon sequestration, boost food production by promoting soil microbes, and help us slow global climate change in the process.
Those are some big claims, and I've often wondered whether anything could really live up to that kind of hype. I wasn't alone.
In fact Albert Bates, author of The Biochar Solution, questioned his publisher's choice of title, suggesting that The Biochar Partial Solution might have been more accurate. Meanwhile George Monbiot issued a withering takedown of some of the grander claims being made by biochar advocates, pointing out that large-scale biochar production could have massive impacts on land use, biodiversity and social justice. And more recently Almuth Ernsting revisited the biochar issue, arguing that research on everything from positive impacts on crop yields to long-term soil carbon sequestration was questionable at best:
Biochar is also promoted as a way of improving crop yields. Those claims, too, are contradicted by science. Field studies reveal highly variable impacts. A recent synthesis review found that in half of all published studies, biochar had either no effect on plants or more worryingly, even suppressed their growth. The author cautioned that due to possible ‘publication bias’, the reported success in 50% of cases should not be taken “as evidence of an overall biochar likelihood of producing positive impacts”.
It certainly seems like the kind of global-scale "biochar as geoengineering" schemes being touted a few years back deserve a healthy dose of skepticism, and according to Ernsting at least, much of the political backing for global biochar initiatives has begun to fade away.
And yet interest among greenies and permaculturists remains high.
Now John Kohler of Growing Your Greens is diving into biochar, visiting Hawaii Biochar to explore how he is making biochar-based soil amendments. Here's a basic rundown of Hunt's biochar production process. (Note that they are currently using a rudimentary pit method of charcoal production, so no energy is being harvested and there will be significant carbon dioxide and other emissions being released into the atmosphere.)
And here he sits down with Josaiah Hunt to talk through application rates, how to make your own, and address some of the criticisms leveled at the industry. (A brief discussion of environmental criticisms starts at 41 minutes - although it doesn't touch on research questioning long-term sequestration).
Now I'm by no means an expert on this topic—so this post is not intended as an authoritative exploration of biochar. Hunt seems like a reasonable, science-minded (though not entirely impartial) fellow, and he clearly believes his product can produce great results. He makes the case that poor or even negative results on crop yields are often the result of over-application and/or the use of raw, rather than matured, biochar. He also argues forcefully that responsible biochar production ought to start with waste biomass, not plantations specifically designed for the purpose of biochar production—something that was echoed in an inconclusive NRDC report on how much biochar might help in the fight against climate change. And he is very open about the fact that this is a nascent industry with some questionable products on the market.
I'd be fascinated to hear from readers whether they've had experiences with biochar, and what the results have been. If anyone has links to further research or resources, they'd be greatly appreciated.
Oh, and for some more positive, science-based news on biochar, check out this blog post (from a company Josaiah hunt works with, Soil Reef) about very early stage research suggesting feeding cows biochar could increase food production and decrease methane too.