Seven Sitkans are taking turns chucking wood scraps into a round metal pit. They’re hauling them from Darren McAvoy’s truck bed where twigs, branches, and logs tower high over the cabin of his pickup truck.
“We don’t need million-dollar high-tech machines to do this really important process of carbon storage,” McAvoy says. “It’s available to anybody in the home, farm, ranch, backyard.”
Or in the outfield of Mt. Edgecumbe High School’s old ballpark. McAvoy, a professor at Utah State University, is in Sitka with the local branch of the University of Alaska Fairbank’s Cooperative Extension Service leading a workshop on how to make biochar. That’s charcoal that stores carbon and improves soil quality.
“If worldwide in the next 30 years all agriculture adopted this approach, we’d have more carbon in our soil than we ever put in our air for the entire industrial revolution,” he says.
Waste wood is often openly burned or left to rot. Both of these scenarios emit 100% of the wood’s carbon. If turned into biochar, McAvoy says only a third goes back into the atmosphere. The rest is stored as a solid of almost pure carbon.
To make biochar, you need large pieces of waste wood and a kiln. McAvoy’s kiln is a simple machine: just two rings of metal kept together by thumb screws. It comes up to his ribs and is about the size of a hot tub.
The bottom is packed with sand to keep air from seeping in. Using a lighter, he ignites small bundles of kindling on top of the spruce and birch branches. Both of these steps are crucial to deprive the kiln of oxygen.
“Pretty soon a flame cap forms over the top of it, and it consumes all the smoke, all the combustibles coming up,” McAvoy says. “So it’s very clean burning.”
Thick smoke and ash billow from the damp wood now roaring with flames.
“It’s more productive and easier and less smoky if the wood is a little bit dry, which is not so easy in Sitka.”
The wood needs to burn for about an hour. That means there’s time for lunch.
“I have hand sanitizer. I have foil. I have bean and cheese and beef and bean burritos. I recommend you grab one and some foil and wrap it up and put it on the top edge of the kiln,” McAvoy says. “Hope your expectations for a good lunch weren’t too high.”
The pile that once poked out above the kiln’s walls has shrunk. Small pieces of dark, black charcoal litter the bottom. The next step requires perfect timing.
“Like when you’re sitting around a campfire late at night, you’re kind of falling asleep, and it poofs out, and it’s just coals,” he says.
That’s when it’s time to quench the burning wood. McAvoy douses the kiln with a garden hose. This stops the biochar from turning to ash. He knows it’s cool enough when he can run his bare hands through the char.
McAvoy says biochar is like a sponge that soaks up compost’s nutrients when mixed together. And there’s another upside according to Andrea Fraga, a gardening teacher at Pacific High School.
“As I get older, my back gets sore. I think about not turning compost piles,” Fraga says. “So if you don’t have to turn them as much, if they’re full of biochar, that’s great.”
For drier climates, the char holds onto water to keep soils moist. Biochar also has its benefits for wetter regions like Southeast Alaska.
“It’s known to hold the nutrients on site and help to prevent the leaching that the heavy rainfall here creates,” he says.
Though it’s not widely used, McAvoy hopes his demonstrations across the country will educate and inspire more people to try it out.
He scrapes up a few handfuls of char and plops it into garbage bags to send home with gardeners. McAvoy hopes his workshop plants a seed for what will grow into a more common practice.
