One of the best short-term strategies for fighting climate change is to stop burning agricultural waste out in the open. But under the right conditions, disposing of farm waste by turning it into biochar, a form of charcoal, can both sequester carbon and improve soil. On farms from Kansas to Kenya, innovators are creating stoves to help farmers take the greatest advantage of the resources they already have on their land.
Biochar is made by heating wood, corn stalks, manure, or a variety of other materials in a chamber devoid of oxygen. While a typical fire would force the carbon in the biological materials to join with oxygen to produce carbon dioxide, a biochar system allows more of the carbon—anywhere from 10 to 50 percent—to stay put. Even after farmers mix biochar with soil, the carbon remains stable and will stay in the ground for hundreds, even thousands, of years. All that carbon could be going to the atmosphere, which means biochar helps permanently capture the carbon that plants suck from the air.
Biochar doesn’t feed plants directly, but it makes soil a friendly environment for biological life. It helps soil retain water and communities of microbes that benefit plants. It keeps nitrogen—necessary for plant growth—from leaching into ground water. Overall, it’s been shown to raise crop yields. This isn’t a secret: Amazonian farmers used this techniques thousands of years ago to prepare thin soils for planting.
Universities like Iowa State and Cornell have begun to look more systematically at biochar. But stoves that create biochar are simple enough that farmers can start using them now. A company called re:char is selling simple kilns that create biochar to farmers in Kenya. Its founder, Jason Aramburu, told Fast Company that his team produces the kilns for $30 or less and charges farmers around the same cost as two bags of fertilizer. In Kansas, David Yarrow, who used to head the Northeast Biochar Association, is working with one farm to build a biochar system that will also heat a greenhouse.
In the absence of oxygen, some of the carbon in the wood or grass turning into biochar turns into natural gas. Well-designed biochar stoves can capture that gas and use it heat the feedstock until it’s fully charred. But it’s also possible to capture that excess fuel and channel it into a heating system.
But for Yarrow, the most important attribute of biochar isn’t its potential to trap carbon or provide renewable energy. “Soil, like the sea, is full of life—or it should be,” he says. “The most important outcome of this strategy is to restore life to soil.”
Photo courtesy of the U.S. Department of Agriculture