Do-it-yourself biochar

Contributed photoPure carbon “biochar” has attracted attention as a means of sequestering carbon in the soil and reducing the amount returned to the atmosphere as carbon dioxide by the decay of organic matter.

It was purely by coincidence, but still it felt right to be speaking to Bill Taylor on Earth Day (April 22). Bill, a committed food grower and environmentalist, was telling me about the history of his involvement with making and using biochar.

I had been hearing about biochar for a number of years, but had never previously bothered to investigate this garden and agricultural soil treatment. So I pricked my ears up when Bill started telling me about what he had been up to recently.

His first job was to explain to me what biochar is. According to Bill, biochar is basically charcoal that has been made by heating wood or other plant wastes in an atmosphere poor in oxygen (a process called pyrolysis). The temperature involved is considerable; ideally, the feed stock should be heated to somewhere around 700-800°F. At this temperature, combustible gases and oils are driven from the feed stock, which is left as more or less pure carbon – “biochar.”

There are a number of ways to process the feed stock, from high tech ovens or “pyrolizers” heated by burning the gases that emerge from the wood or other materials, to the very low tech, the latter being the method Bill favors. His current method, in fact, is not so different from the one that prehistoric Amazonian peoples used to make the terra preta, the “black earth” that characterizes certain areas of the Amazon basin.

Tropical soils are commonly poor because the combination of heat and moisture leads to rapid decomposition of most organic materials such as fallen wood or leaf litter, and the frequent heavy rains leach out minerals. What the indigenous peoples learned was that converting the organic materials to charcoal and then mixing them with manure and household debris, could contribute a long-lasting benefit to the soil. Indeed, the charcoal will persist for centuries, even in tropical conditions, enhancing soil fertility, especially in the case of acidic soils, as well as providing a number of other benefits, such as improved plant growth, a better environment for soil fungal growth, and protection against some plant diseases.

More recently, biochar has attracted attention as a means of sequestering carbon in the soil and reducing the amount returned to the atmosphere as carbon dioxide by the decay of organic matter. Carbon dioxide is the principal gas leading to the heating of the atmosphere by the greenhouse effect, and the production of biochar is seen by its supporters as a method for combating global warming.

Bill Taylor learned about biochar when he and his wife Jaye Alison Moscariello were operating a ranch in Redwood Valley, California, and he brought the knowledge with him when he and Jaye moved to the Berkshire Hills of western Massachusetts last year. As the couple installs an orchard and food gardens around their house, they’ve had a lot of clean-up to do, including the removal of a number of storm-felled trees.

These Bill has treated in a manner he copied from the old-time charcoal burners who left their combustion pits all through the woods surrounding his home in Sandisfield. Bill excavated a circular pit 4 feet wide and 4 1/2 feet deep. He filled it with the waste wood, and then on a snowy day in mid-April (that was when the local fire chief would issue a burn permit), Bill built a fire on top. He used the spray from a hose to damp the fire when it threatened to burn too vigorously – the object was to heat the wood below, not set it afire. From time to time, Bill would turn up the wood to inspect its progress, and when the thinner pieces were carbonized, he transferred the thicker, unfinished chunks to a second pit and continued the burn there, while he wet the first pit to stop its combustion. In 2 ½ hours he was done.

Later, after the biochar cooled, he crushed it with a tamper and, when I came to inspect, Bill showed me how he dug the granules into a pile of cow manure. When this has composted for a year, Bill says, he will add it to any new garden beds he creates or scatter it over existing plantings to let the worms carry it down. There it will remain, a thousand years or more, doing its part to combat global warming.

Thomas Christopher is a volunteer at Berkshire Botanical Garden and is the author or co-author of more than a dozen books.

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