Roast Your Compost And Save The World?


Img_0983 Just as the wildfires in California were raging most ferociously this week, I picked up New Scientist magazine and learned something that probably offers no consolation whatsoever for the scorched earth many Southern Californians are now confronting: It’s possible to burn a landscape in a way that yields something extremely valuable.  It’s called biochar, the end product of slowly combusting organic matter in an oxygen-poor environment. 

Biochar seems to be a key ingredient of terra preta, the super-fertile soil of the Amazon created by some very smart pre-Colombian gardeners.  Now biochar could conceivably help us to stop cooking the earth, because the charring process can be used to generate biofuels or electricity.  Meanwhile, the leftover char locks up carbon underground almost indefinitely–carbon that might otherwise make its way into the atmosphere.  At the same time, it encourages the robust growth of plants, which, in turn, take CO2 out of the air and turn into oxygen.

In fact, an article in Nature says that a number of scientists are extremely interested in biochar as a means to combat global warming:

Johannes Lehmann of Cornell University in Ithaca, New York…estimates that by the end of this century terra preta schemes, in combination with biofuel programmes, could store up to 9.5 billion tonnes of carbon a year — more than is emitted by all today’s fossil-fuel use.

Organic matter that’s smoldered rather than burned is much better at locking in carbon and creating a long-term positive change in the quality of the soil.  Still, I’ve long scattered the detritus of my fireplace–a mix of ash and charcoal–underneath my lilacs and clematis to make the soil more alkaline for them, and noticed how cheerful they look about it.

The Nature piece also mentions the work of Danny Day, the entrepreneur who founded a company called Eprida, which makes equipment for generating biofuels and biochar.

Originally, Day was mostly interested in making biofuel; the char was just something he threw out, or used to make carbon filters. Then he discovered that his employees were reaping the culinary benefits of the enormous turnips that had sprung up on the piles of char lying around at the plant.

Now Day is making a biochar-heavy fertilizer, too.  I always love a story in which food-obsessed vegetable gardeners drive technological progress across the globe.


  1. While the biochar locks carbon in the earth, what is the impact to the atmosphere of the burning? I know the article says that it’s a way to combat global warming but my environmental science classes in college tell me that slash and burn agirculture, and the burning of wood are one of the big contributors to not only air pollution but also those dreaded greenhouse gases.

    And, we need to also remember that while slash and burn agriculture, practiced in the amazon, adds immediate nutrients to the soil, the nutrients are also quickly depleted, causing the amazonian farmers to move onto a new plot and repeat the practice.

    I think the idea may be good, but is is it sustainable to the entire ecosystem? I look forward to learning more.

  2. Rachel, I took a look at some of the work of the Cornell scientist mentioned in the story. I learned that slash and burn is a short-lived boost. But slash and char–in other words, combust the organic material slowly, incompletely, without enough oxygen for a ferocious burn–offers a soil improvement that can last hundreds of years.

  3. Michele-

    Oh, how interesting! Thanks for the info–that makes a huge difference! I’d imagine slash and char would be less polluting, too. After all, in a fire pit you can see all the smoke from burning the wood, but once the fire is embers, not as much smoke is produced.

  4. That is fascinating. Our local government put together a big proposal to get a carbon sequestering project that would involve pumping CO2 into our many miles of abandoned deep coal mines. Had some folks a tad nervous, because if it leaked out, there could be much death. Not because it is a deadly gas, but because it replaces the oxygen in the air. (We did not get the project, Texas did, gee, I wonder why…). I like this way much more.

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