Make Biochar — this Ancient Technique Will Improve Your Soil

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I’m part of the Smokey-the-Bear generation, raised on phrases like “learn not to burn,” so it took me a while to warm up to the idea of using semi-open burning as a soil-building technique. Unrestrained open burning releases 95 percent or more of the carbon in the wood, weeds or whatever else that goes up in smoke. However, low-temperature controlled burning to create biochar, called pyrolysis, retains much more carbon (about 50 percent) in the initial burning phase. Carbon release is cut even more when the biochar becomes part of the soil, where it may reduce the production of greenhouse gases including methane and nitrous oxide. This charcoal releases its carbon 10 to 100 times slower than rotting organic matter. As long as it is done correctly, controlled charring of weeds, pruned limbs and other hard-to-compost forms of organic matter, and then using the biochar as a soil or compost amendment, can result in a zero emission carbon cycling system.

Burning responsibly requires simple common sense. Check with your local fire department to make sure you have any necessary permits, wait as long as you must to get damp, windless weather, and monitor the fire until it’s dead.

The Bigger Picture

If global warming is to be slowed, we must find ways to reduce the loss of carbon into the atmosphere. In the dark earths of the Amazon, and in million-year-old charcoal deposits beneath the Pacific Ocean, charcoal has proven its ability to bring carbon release almost to a standstill. If each of one million farmers around the globe incorporated biochar into 160 acres of land, the amount of carbon locked away in the Earth’s soil would increase five-fold.

But there’s more. What if you generate energy by burning a renewable biomass crop (like wood, corn, peanut hulls, bamboo, willow or whatever), while also producing biochar that is then stashed away by using it as a soil amendment? (For an example, see the Archive article, Mother’s Woodburning Truck, about wood-gas generators.) The carbon recovery numbers in such a system make it the only biomass model found thus far that can produce energy without a net release of carbon. Research teams around the world are scrambling to work out the details of these elegantly Earth-based systems.

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