(A similar version of this article has been published in GCFM's February issue of Maine Grows)
By Peter Arnold
A few years ago, a friend in British Columbia, where my wife and I spent a dozen winters, asked me to help her with a project – to make a large amount of compost and include biochar. I’ve been involved with environmental and renewable energy circles for decades and had only heard about biochar as a way to sequester CO2. Biochar is being utilized in several industries but using it as a soil amendment and adding it to compost was a new idea to me and gave the wet winter a focus on the little rainy island where we lived.
We had most of the ingredients on hand for the project including 20 big bails of spoiled hay and a collection of cow manure both old and fresh daily. We had no biochar and making it was my task to figure out. Over that winter and since, I have built and used six methods to come up with the one I now use.
There are hundreds of different strategies for making biochar, including digging a pit in the dirt plus lots of homemade contraptions like mine, as well as very sophisticated commercial and industrial scale equipment. There are also several universities and for-profit industries researching biochar, including the Agriculture Research Service at the US Department of Agriculture. But why the interest?
What is Biochar?
The term ‘biochar’ is fairly new and was first used in 1998. The actual material and process is ancient and has been used for thousands of years.
Biochar has two very important properties:
1. It has an extremely stable molecular structure. Because of the stability of the biochar structure, it is able to capture and store (sequester) carbon for thousands of years.
2. It is extremely adsorptive. Biochar is a lightweight carbon-rich charcoal-like substance produced from heating carbon-based materials in a low oxygen environment (pyrolysis). Biochar is enormously porous and has a huge internal surface area because of the pyrolysis process. That vast internal surface structure gives it the ability to attract and retain moisture and nutrients (adsorptive). One fourth (1/4) an ounce of biochar (about the weight of a quarter) can have an internal surface area the size of a football field!
It turns out that the millions of electrically charged micropores in biochar attract and retain what we gardeners want in our soil – moisture and nutrients and keeps them available to plants over a longer period of time.
Though few people have heard of biochar by name, most of us know civilizations all over the planet burned crops to make their soils more fertile – at least for a little while. However, after a few years using slash and burn techniques, the soils were depleted, had lost all fertility and eroded easily and had to be abandoned. But in 1966 a soil scientist documented areas of land in the Amazon basin with soils that were three times more fertile and higher in organic and nutrient content than the surrounding soils.
The fertile soils, quite dark in color, were named Terra Preta, meaning dark earth in Portuguese. Terra Preta soils were created in the Amazon basin 2500 years ago by pre-Columbian farming communities around 450 BCE and they are still fertile. Those soils contain evidence of charcoal plus intentional additions of manure, shells, algae and pottery.
How is Biochar Made?
Basically, biochar can be made simply by piling any organic material, setting it on fire and covering it to reduce the oxygen. I like to make biochar during the winter months using the brush piles I collect during the growing season. Any biomass can be used to make biochar and I’ve used everything from Douglas fir saplings, to maple branches, to bittersweet vines and brambles. A Japanese friend said his parents make biochar by burning rice hulls in Japan; another friend burns scraps from building furniture. At this stage of my biochar-making, I prefer to use small diameter branches because the product is finer and easiest to add to my compost. After making several iterations of burn barrels, I use either a 55 gallon barrel for smaller piles or a 250 gallon old oil tank for larger burns or if we are doing a garden club demonstration. Several techniques just use a pit dug into the ground.
The point is to be able to control the rate of burn and to limit the combustion by reducing the amount of oxygen. At the right point, the fire is extinguished (quenched) and left to cool. When possible, I prefer to quench with snow, if not water works every time. The key is to stop the combustion. If it burns to ashes, it is NOT biochar!
Raw biochar is not instantly ready for use.
Remember biochar lasts thousands of years in the soil and it is not in a hurry, even if you are. Fresh biochar is called raw biochar. Biochar’s trick is to fill and colonize the surface of its millions of micropores with water and nutrients - which takes time. This process is called inoculation or charging it with nutrients. The Fedco catalog describes biochar as, “a dream home for beneficial bacteria and fungi and prevents essential plant nutrients from leaching out of the root zone.” This is exactly why the Loma Preta soils have remained fertile for 2500 years.
How to use biochar?
If you are in a hurry, you can inoculate your biochar by making water and nutrients readily available. The best and easiest way that I’ve found is to mix the biochar directly into my compost as I make it and let it do its magic!
Mixing the biochar into the compost allows the moisture and nutrients from the compost to ‘inoculate’ the vast biochar network of pores so that when added into garden beds it is ready to go to work. The ratios I use for compost are 3 units carbon-rich browns to 1 unit of nitrogen-rich greens to 2 units of biochar.
Another way to inoculate the biochar is to soak it for a week in any liquid nutrient such as compost tea, worm castings or seaweed extract. You can also purchase inoculated biochar.
An optimal ratio for most applications is 10% biochar (1 part biochar to 9 parts soil) in the top 6 inches. You can get to this ratio by spreading one-half (½) inch of biochar over the topsoil and tilling. However, using as little as 2% biochar in your soil is beneficial!
For long term soil improvement, raw biochar that has not been inoculated can be directly spread onto fallow land. Raw biochar should not be used on active fields because soil fertility is initially reduced for up to two years by the biochar temporarily up-taking available soil nutrients. I have not used biochar this way but research says it can be applied directly to soils, knowing it will take 2-3 years before the native soils can colonize the raw biochar. The improvement in crop production after the biochar is incorporated into the soil is reported up to 30% increase.
Where can I get Biochar?
Biochar is commercially available. You can buy it in small quantities at: Fedco, Tractor Supply, Lowes, Home Depot, Walmart, and Amazon or in large quantities at: FedCo or Standard Biocarbon. I noticed that biochar products on the Fedco site note they are MOFGA approved. OR you can make your own!
Besides agricultural benefits, how else is biochar used?
Biochar can be used in bioremediation and is a potential as a sorbent for PFAs.
The heat produced during biochar production can be used to generate electricity.
Biochar’s ability to sequester CO2 can be sold as carbon credits.
Interested in more information on Biochar?
Peter Arnold is a member of the Garden Club of Wiscasset. Besides being an avid gardener, he has a long tradition of unique interests in the natural world including: alternative building, renewable energy of many forms, composting, making biochar, growing microgreens, seaweed farming, foraging and wild-crafting. His approach is simple, “look around and make use of what’s close-by”.
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