by Connie Oswald Stofko
The Amazon basin in general has poor soil, but it has some areas with amazingly fertile soil. Those fertile soils were created thousands of years ago by people using slash-and-burn agriculture. What was left behind from the burned plant material created the soil called terra preta, or black earth.
And that soil, thousands of years later, can still be farmed today.
Now we’re trying to replicate those fertile soils by using biochar, a kind of charcoal that not only can be helpful in your garden, but may help to mitigate climate change.
You can learn more about biochar at an event called “A Carbon Experience” from 11:30 a.m. to 4 p.m. Sunday, Oct. 1 at Henry’s Gardens, 7884 Sisson Hwy., Eden.
It is being held by the Biochar Coalition. The presenters will be John Maher of Lake View (near Hamburg), a board member with the Biochar Coalition, and Ken Scherer of Northern California, executive director and secretary of the coalition. There will be a demonstration of pyrolysis, the process used to create biochar.
Benefits of biochar
- Biochar can help move nutrients through the soil. (This has to do with chemistry and soil electrical conductivity.) “And it works instantly, as soon as you bury the biochar,” Scherer said. “It’s good especially if you have clay—biochar helps clay. It’s like they’re best friends. That’s why I see such a value in biochar. It unlocks the soil.”
- Biochar can increase the quantity and activity of microbes in the soil, which are necessary for plant health.
- It is porous, absorbing and retaining water and nutrients.
- Because it is very stable, biochar doesn’t decompose the way other plant material does. It can lock the carbon in the soil for a very long time.
- Less fertilizer is needed. That’s good because synthetic fertilizers produce greenhouse gases when they are manufactured and when they are used, and they also damage microorganisms.
On a large scale, biochar can:
- Be made from forest trees that need to be cut down because of insect and disease outbreaks or in a controlled burn to suppress wildfires. Currently, those trees are often burned in slash piles that can contribute to air pollution, generate greenhouse gases and damage the soil.
- Transform sewage and other waste into a useful resource.
- Possibly clean up polluted soil.
- Possibly become a source of renewable energy.
How biochar is made
Biochar is created in a process called pyrolysis.
Plant material, such as wood, is heated in the absence of oxygen (or with little oxygen). Animal material and even manure can also be used.
Carbon dioxide and methane, two greenhouse gases, aren’t released into the atmosphere (or very little is released) during the pyrolysis process.
“It keeps the carbon out of the air and in the soil where we need it to be,” Scherer said.
The simplest way to make biochar is with a campfire.
Note: Don’t make a campfire in a city or suburban yard. If you think you can do this in your rural landscape, please contact your local fire department to make sure it’s within your town’s regulations.
When you’re ready to make the campfire, “Start the fire on the top; you don’t start it on the bottom,” Scherer said.
Doing it this way creates a flame cap; that is, a cap made of flames. You’ve probably seen a tall smokestack on a factory with flames shooting out of the top. The factory is burning pollution so they can meet air quality tests, he said. In the same way, the flames on the top of your campfire will catch and burn off most of the carbon dioxide and methane.
Eventually you will get two fires: a hot fire on the top and another fire on the bottom. When the two fires meet, everything is burning equally. Now you have a char bed. Quench the char bed; that is, spray it with water. That stops the pyrolysis process.
“Boom, there’s your biochar,” Scherer said. “You just did a really good thing for the environment. Even though you’re not going to get a medal, you can give yourself a pat on the back because you know you’ve done some good.”
It’s important that you don’t let the let the wood burn too long. You want to stop the burning process as soon as you have biochar; if you see ash, it has burned too long.
“Quench your coals; that’s the main thing,” he said. “‘Quench your coals. Don’t be an ash hole’.”
If you mistakenly let your fire go to the ash stage, you can use the ashes in your garden, he said. But don’t add a lot—ash is highly alkaline. That could throw the pH of your soil out of whack and harm your plants.
The kiln is started the same way as the campfire, by starting the fire from the top, not the bottom, then loads of wood are added periodically. That not only adds more material, but the flaming top–the flame cap–restricts oxygen from the ember and biochar layers in the kiln. Fire on the top is getting oxygen for the flames, but none of the material below it is getting oxygen. In addition, gases from the ember layer are being burned in the flames and help the fire get hotter. Carbon dioxide and methane being emitted from the lower layers are getting burned up in the flame cap.
Another difference is that, with the campfire, there is no barrier, so oxygen is able to come in from the side. The diagram above illustrates that the sides of the kiln don’t allow oxygen to leak in; the only air flow is from the top. (There is a heat shield surrounding the kiln to protect people from the extreme heat. The air flow from the ground up is caused by the space between the heat shield and kiln. As the air in that space heats up, it rises up to the flames.)
The kiln is more efficient than the campfire, producing a higher quality and quantity of biochar.
“A proper biochar fire should have no smoke, well, a little to no smoke,” Maher said. “There’s always some moisture.”
The additional loads of wood block the oxygen from the layers below so they can stop combusting.
When you’re done adding material or your kiln is full, watch the last layer. When it has glowing red embers and you start to see ash, it’s done. Quench it.
Still another example of making biochar is a totally closed process, which you can see in this video from Cornell University.
There are many other kinds of equipment that people use, and new kinds are being created.
“There’s so much room for ingenuity,” Maher said.