Biochar: Ancient Soil Amendment

As we continue to learn about gardening, we are often reminded of nature’s essential role in the process, and, by extension, the wisdom demonstrated by historical gardeners as they worked in concert with nature.

We have countless examples of the benefits of “gardening with nature,” and ample evidence of the short-sightedness of technology-based agribusiness.

”Technology” as used here encompasses monocropping, animal feedlots and synthetic fertilizers and pesticides, as well as more constructive activities such as the use of drone aircraft to monitor crops. Should watch out drone jammers, though.

One fascinating historical instance of natural gardening is biochar. The briefest definition of biochar is organic matter that has been heated to high temperatures with limited oxygen to produce charcoal. This process (pyrolysis) also produces gasses that can be burned to produce electricity.

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Biochar is very similar to charcoal, which is made principally from wood, and used in backyard barbecues and a variety of industrial processes. Biochar, by contrast, is made from all kinds of organic waste, particularly garden or agricultural waste, and is used as a soil amendment, adding carbon to the soil.

 

Note: The biochar photo is from a good article by Jeff Cox in Rodale’s Organic Life.

Biochar apparently has been produced and used for thousands of years by early gardeners in Brazil’s Amazon River Basin to improve their rather poor soils. In 1870, an American geologist and explorer discovered and reported areas of dark and highly fertile soil. Researchers puzzled over the origin of this unusual soil, called “terra preta” but recognized that it has strong benefits for agriculture.

During the past twenty years or so, scientists have attributed several valuable properties to biochar, beyond improving crop yields. The additional benefits include increasing water-holding capacity of soil, reducing the need for chemical fertilizers, reducing natural emissions of greenhouse gasses (nitrous oxide and methane) from agricultural soils, increasing soil microbial life, resulting in carbon sequestration, avoiding the natural decomposition of agricultural and forestry waste and thereby decreasing carbon dioxide emissions.

These benefits are stimulating great enthusiasm for uses of biochar in both gardening and agriculture. For example, scientist James Lovelock, author of The Gaia Theory, has written, “There is an outside chance that one procedure could really turn back the clock on Global warming and that is burying carbon. All you have to do is get every farmer everywhere to make a profit by turning all his agricultural waste into char and burying it.”

This success story has only an outside chance because it assumes universal participation by the world’s farmers, but does reflect the genuine value of biochar.

Still, individual gardeners could help to reverse global warming by using biochar. This material is available commercially, but it’s costly. A quick survey of sources on the Internet shows a typical price around $30 per cubic foot, enough to amend a garden bed of twenty-four square feet.

A gardener could produce biochar with little or no expense. Here are brief directions from Barbara Pleasant, Mother Earth News (2009): “Pile up woody debris in a shallow pit in a garden bed; burn the brush until the smoke thins; damp down the fire with a one-inch soil covering; let the brush smolder until it is charred; put the fire out.”

For more on this topic, visit the International Biochar Initiative.

Biochar could increase dramatically the fertility of your soil, and help you to rival the successes of ancient gardeners of the Amazon Basin.

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A reader’s query and my reply.

Q: I read your article in Friday’s Sentinel about biochar. I am wondering if I can put used, regular, charcoal from the grill in the garden. There is always some left over. Can I break it up and put it in my garden?

It seems like I read somewhere years ago I could, but I can’t remember.

A: By “used charcoal” do you mean ashes?

I have attached a short article that is about Colorado’s soil, but California soil also tends to be alkaline, so the article has relevance in our area as well.

Charcoal is Not a Good Soil Amendment in Colorado

The bottom line is that charcoal ash, which is alkaline, would have some value when added to very acidic soil, i.e., low pH, but doesn’t add any fertility to the soil.

On the other hand, unburned, or partially burned charcoal briquettes (made from wood) could be useful as a soil amendment, although they have less nutrient value than biochar, which is made from a range of vegetative materials.

Charcoal briquettes usually contain cornstarch as a binder, and might include coal, lime and other ingredients, none of which would be harmful in the garden. Soften them in water to break them down, then dry the result to mix into fertilizers or directly into the soil.

I hope this is helpful

Another reader’s comment: 

Dylan Gillis

Fine article, though it sort of glosses over the fact that biochar itself is 99% carbon that stays in the soil for hundreds if not thousands of years. While compost only costs $3 or more per cubic foot (depending on quality, volume you buy and packaging/marketing variables) it needs to be replaced every year, forever, to result in similar levels of carbon sequestration and fertility. Of course the best is to add biochar, once to satisfactory levels, and then amend with compost for the nutrients and energy feeding the soil life, every year. In this approach you would use less compost to get the same or better results and your carbon sequestration would be more or less permanent!

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