GARDENING WITH THE MASTERS: Biochar — More valuable than gold for cultivating nutrient-rich soil

One of the great things about being a Master Gardener is the need for research. (I know…former English teacher…maybe it’s an acquired habit.) And one of the best things about research is coming across something you knew nothing about — by name, anyway. And so to Terra Preta, the “dark Earth” utilized by Amerindians in the Amazon Basin, apparently eons before their discovery by Spanish explorer Francisco de Orellana in 1542. The name Terra preta del indio is the full term for the rich soils produced from 500 to 2500 years ago B.C. Why do we care about these ancient South Americans? Because what they created then we can learn from now.

Obviously, we need nutrient-rich, deeply cultivated, well-draining soil for landscaping or crop growing. We also know that we live in clay-based Georgia… ‘nuff said. Scientists know that desirable dark rich soil is due to plant carbons, which can remain in the soil for thousands of years. They believe that ancient Amerindians used a method called “slash and char.” It’s pretty simple really. You’ve heard of “slash and burn” to clear land … but what if you didn’t burn the vegetative material completely? What if you just charred it (think campfires) and then buried it? Plenty of evidence has shown that this method enabled ancient societies to flourish by burning their fields and thus nurture the soil into lasting productivity. (As a side note: later explorers looking for gold found no evidence that such societies even existed. Researchers hypothesize that Orellana’s expedition itself may have brought diseases that the indigenous people were unable to withstand. Yet flyover examination has shown striped patterns as relics of a system of raised beds.)

What an ancient civilization knew continues to be researched by scientists today. We don’t know how the exact process worked, but we can experiment with what is now more commonly called “biochar.” It is a work in process: Cornell is one leading research university. Due to its ability to attract and retain water, biochar is said to be hygroscopic. It is created using a process called pyrolysis. I can’t resist new vocabulary, but to be honest it really just means charring solids at high heat. You burn stuff, and if you don’t burn it all the way into oblivion, what you end up with is … char. Charring removes hydrogen and oxygen, leaving carbon, and that locks into the soil, making it highly fertile and long-lasting.

Thus, the application to us today. Biochar enhances plant growth while reducing the need for fertilizers. It reduces acidity (which can be a plus here in Georgia), and a long list of other attributes that scientists are interested in — things like soil microbial respiration. We laymen don’t worry so much about how microbes breathe, just know that they’re good to have down in the dirt. The application to the agriculture community is obvious: greater crop yields. Biochar enthusiasts agree that the raw charcoal should be processed further before you add it to your garden. They suggest adding it to your compost pile or soaking with compost tea.

How do you get started? Home pyrolysis is fairly simple. You can use something called a burn barrel, an upright steel barrel open in one end. When it is almost full, you put the lid on tightly (keep a small vent) and let it sit for 2-3 days. Fill it with yard debris, felled trees, anything vegetative. (You can even use bones, which when burned this way produce desirable phosphorus.) But I have to tell you, this and other methods produce highly variable results in terms of the volume and quality of what you create. It strikes me as a lot of trouble, especially when you factor in the need to be careful about saturating the neighborhood with smoke. The solution? Go to the site-that-sells-everything online. Type in “biochar soil amendment.” You’ll be all set.

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