Espousing the benefits of biochar

Posted March 06, 2009, at 5:58 p.m.

Like most of us, Eastport resident George Hoche waits for the thaw. Waiting, he thinks about his vegetable garden and his greenhouse. He thinks about the community food garden that he and other Master Gardener Volunteers are starting this year to support the local food pantry.

George also thinks about firing up a self-made oil-drum furnace that now stands buried under ice and snow across the driveway in front of his home. He is eager to make more biochar.

One morning last week, I stopped by George’s home to drop off an article on biochar just published in the journal Orion. The article, “Plants Suck,” written by Middlebury College scholar Bill McKibben, reminds us that plants suck carbon dioxide out of the atmosphere, storing it in their tissues in the form of cellulose and lignin, the primary molecules of wood, as well as starch and other compounds. When plants die and decay, or when wood or other plant tissues are completely burned, this carbon is returned to the atmosphere as carbon dioxide.

The incomplete combustion of these plant tissues, however, produces a form of carbon called biochar. Anyone who heats with a wood stove knows biochar, the small charcoal-like lumps found under the ashes where combustion is hindered by a lack of oxygen. Lasting for years in the soil, biochar keeps carbon that would have been returned to the atmosphere out of circulation.

Handing the article to George, I pointed to McKibben’s words, “If you could continually turn organic material into biochar, you could reverse the history of the last two hundred years.” McKibben was talking about the last 200 years of human activity — the burning of fossil fuels, including gasoline, natural gas and coal — that has caused the increase in atmospheric carbon dioxide levels responsible for Earth’s current global warming crisis.

George calls his method of making biochar the “indirect method” because the feedstock, usually hardwood bark or wood chips, is never in direct contact with the flame. By limiting the amount of oxygen reaching the feedstock, incomplete combustion produces plenty of biochar. George also equipped his furnace with an afterburner that returns waste gases back to the flame for complete combustion. Recycling of the waste gases contributes to operation of the furnace.

The biochar is removed from the furnace and, after cooling, crushed to a fine granular texture before being used or stored. Hardwood bark crushes easier than other feedstocks.

As a gardener, George understands the importance of building healthy soil. Shelves in his work area are crammed with books, soil-testing equipment and samples of the biochar he has produced from various feedstocks. He views biochar as a soil amendment that can improve soil texture, hold essential plant nutrients in the soil, and increase soil populations of beneficial microorganisms. His views are echoed by research reports from universities around the world.

George has experimented with application rates and determined that lower levels, around two ounces per square foot of soil (125 pounds per 1,000 square feet) work best in terms of soil nutrient levels and plant growth. Higher rates result in excessive nitrogen and potassium levels. He has also noticed improved soil structure with use of biochar.

What is the future of biochar? McKibben believes we can use biochar to sequester significant amounts of carbon in the soil, the first real attempt at “scrubbing the atmosphere.” He envisions mobile biochar-producing furnaces patrolling forests devastated by storms or insect attacks.

George is planning additional field trials of his biochar. He also plans to use biochar this spring to improve the soil in the Master Gardener food garden project. He envisions a day when biochar is as common as peat moss at the local garden center.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and number.

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