Garden Like a Boss: Biochar 101
Here’s the scoop about the Next New Thing in the gardening world.
—by James Loomis
Biochar. This soil amendment has accrued more accolades than perhaps any other soil amendment since the much heralded release of manure. An eco-hipster synonym for charcoal, it is the end product created by burning a fuel source in a restricted oxygen environment, a process known as pyrolysis.
Modern pyrolosis is not the same as burning, and emissions can be almost negligible. Wood, agricultural waste and even bones can be transformed into a material that is a highly stable latticework incredibly high in carbon.
The first use of charcoal as a soil amendment is attributed to the peoples who inhabited the pre-Columbian Amazon. By burying smoldering agricultural wastes rather than burning them completely, they achieved a crude form of pyrolysis. We also see some evidence of biochar use from the Mesoamerican farming practice of creating milpas, an ecosystem succession farming strategy where small plots of jungle were slashed and burned or charred, then over the course of time allowed to return to jungle. This style of farming is one of the most sustainable agricultural models created to date, and benefits from the use of biochar.
Perhaps the most compelling argument for the use of biochar is that, when buried in the soil, it can be a powerful tool in the race to sequester carbon from the atmosphere. Proponents also claim that it can increase a soil’s water retention capacity, combat soilborne diseases, enhance soil biology and promote fertility. These claims are not without their detractors, however, so let’s dive in and see when and where biochar has promise.
The carbon in biochar remains quite stable when buried, and can remain locked there for decades, centuries or even millennia. While the process is generally accepted as carbon negative, how it is made and the origin of the fuel source is key to whether it is truly beneficial for the environment.
While undergoing the pyrolysis process, our fuel generates heat, as well as a variety of solid (biochar), liquid (bio-oil) and gas (wood gas) components. When this process is fully harnessed, we can not only generate biochar but also utilize the energy from the combustion of the oil and gas components as well. This energy can offset a more polluting source, and is a great strategy for the world’s off-grid citizens to fuel their kitchens.
When done correctly, this process becomes carbon negative, as pyrolysis is a much cleaner alternative to burning, and more carbon is sequestered into the soil than is released into the atmosphere.
Biochar production makes the most sense when our fuel source is diverted from the waste stream, particularly a source that otherwise would be simply burned.
Britney Hunter from the Utah State University Extension Office told me of plans by the US Forest Service to explore the option of generating biochar from the 40,000 acres a year that get burned to create fire breaks.
Hunter herself is working with local orchardists to produce biochar from the large stocks of waste wood from pruning they currently burn.
I am personally working on a collaboration with Chris Erickson of Arborworks Tree Care and the team at Salacia Farm in Lehi to use a bio burner retort to generate biochar from waste wood, while capturing the energy to heat the water in their 27,000-gallon aquaponic system.
Unfortunately, the hype around biochar’s ability to sequester carbon when compared to burning has led to a push for large scale biochar production, which includes plans for large scale industrial agriculture projects to generate feedstocks. Massive monocultures which devastate biodiverse landscapes to simply grow fuels for biochar run the risk of outweighing any benefit from carbon sequestration; much like our current domestic biofuel production.
Increase soil’s water-holding capacity
Since biochar has a tremendous amount of open pore space in its structure, it is able to retain water like a sponge. In arid climates such as our own, this is perhaps the single best reason a gardener would choose to utilize it. Turf with 2-4% biochar incorporated into the soil has shown significant resilience to drought over control groups.
Combat soilborne diseases
Charcoal is an amazing antimicrobial material. In a survival situation, it makes a reliable agent to filter pathogens from water. It can be ingested to help combat stomach sickness caused by harmful microbes. In studies where biochar was incorporated into soils with disease organisms present, plants showed a marked improvement over controls. Is this due to the anti-microbial power of the biochar combatting the pathogens present in the soil? Perhaps, which leads us to the next on our list….
Enhancing soil microbiology
Remember that charcoal is a powerful anti-microbial substance, and it’s clear it won’t be getting colonized by beneficial bacteria, nematodes or mycelium any time soon. In fact, our microbial soil community will most likely suffer quite an initial assault. To combat this, soil food web scientist Elaine Ingham recommends that any application of biochar first be soaked in a powerful compost tea, in a strategy aimed at overwhelming the anti-microbial capacity of the char. Since biochar is often incorporated into the soil through tillage or burying, we are also disrupting the microbes further.
Enhance soil fertility
Since soil microbes fuel the cycling of nutrients in the soil, and biochar is antimicrobial, it makes sense that most crops show a dip in plant growth initially, but this often returns to normal after a few months to a year following application. While biochar can improve soil structure, especially in sandy soils, this does not necessarily equate with fertility. Some crops show improved yields over time, others less. More long term scientific studies need to be conducted.
While biochar appears quite effective at carbon sequestration, there are many variables to consider; source material, soil type, climate and how it was produced.
The USU extension office is currently conducting a three-year biochar trial at four sites in Davis County and the USU Botanical Gardens. They’ll be testing for yields as well as water retention. They also are conducting a greenhouse trial on disease resistance, in soils inoculated with fusarium and phytopthera.
Since a lot of study still needs to be conducted that’s specific to our bioregion, now is a great time to experiment! In future months we’ll tell you how you can participate, keep records, take notes on your observations, and share your research with your fellow gardeners.
James Loomis operates Salacia Farms, a Lehi organic farm offering winter CSA (community-suppored Agriculture) shares. He also teaches the “Beyond Organic” series: “Regenerative Agriculture and Urban Homesteading.” Stay tuned to the CATALYST Weekly Reader for details. (December class is full.)
Follow the USU Extension study: www.UtahBiomassResources.org
Biochar: The Home Gardener’s Primer
(PDF available online here: http://bit.ly/1QJUv4i