Make Biochar, Save Oceans

In case you need another reason to make biochar, have a look at the oceanic carbon cycle.

As we breathe, so does the ocean. Gases move back and forth through the ocean surface. This is how fish get oxygen, which they extract from the water through their gills. The constant exchange of gases between water and air keeps carbon dioxide and oxygen at the same proportion above and below the surface.

As carbon dioxide builds up in the atmosphere, it builds up proportionately in seawater. But dissolved CO2 reacts with water to form carbonic acid (H2CO3), leaving room for more CO2 to dissolve. As it does, carbonic acid increases, resulting in a more acidic ocean. This is now happening more rapidly, raising alarms among scientists.

Without shells, no oysters. (Photo: Cavan Images)

Sea shells are made of calcium carbonate. The shells are formed by the organisms that inhabit them; coral, urchins, and certain plankton are the same. All the reefs and shells in the ocean are formed by marine organisms, which depend on their ability to extract carbonate ions from the water in order to manufacture calcium carbonate. But ocean acidity reduces the number of carbonate ions, making it harder for these animals to build and maintain their shells. This has started to result in a decline in marine organisms that depend on making carbonate, followed by a decline in animals further along the food chain.

Similar to proposals for extracting carbon from the air with energy-intensive technology, there have now been others to directly restore ocean pH by adding large amounts of basic compounds. IMO these are untested, dubious and risky initiatives aimed at maintaining fossil fuel extraction and use, whereas sequestering carbon derived from photosynthesis and weaning ourselves from oil dependency are clear solutions. Diverting carbon to long-term storage is one of the main reasons we pyrolyze excess plant material.

So when you’re making biochar, you’re not just counteracting global warming. You’re helping to save the life in the ocean, along with every life form that feeds on that abundance.

Another Look at Grinding Biochar

Charcoal comes out of the kiln in different sizes, many of which are too big for amending garden soil. (There does not seem to be a too-small size, considering that the particles in terra preta had to be identified with a microscope.) A cornerstone of my biochar practice has been to reduce the charcoal down to 1/4” or less, according to instructions from Paul Taylor. There is a theoretical maximum surface-to-volume ratio at which the char still allows water, nutrients and microbes to fully permeate it, and 1/4” is the number Paul gave me.

The grinder that I designed and built in 2018 was effective at reducing char to this size with only a hand crank, well suited to life in an off-grid neighborhood with limited power.

Decking screws inserted in a lathed 2-1/4” dowel are backed out to rip the char, just clearing the 1/4’ gap. Works in both directions. Hopper is oak plywood; wheel came from a meat grinder.

I would have liked to find a method of grinding that didn’t require hours to build, but the solutions I saw online tended toward inefficiency, unsustainability and health threats. Mine yields a cubic yard in about three hours and propels the toxic dust into the bucket through the lid to which it’s attached.

The wooden parts gradually wore down. I was prepared to replace them this year, but two new factors had come into play. In 2021 we upgraded our solar system and could now consider an electric grinder. Secondly, we had found 1/4” biochar too large for our liking in the garden.

On a listserv to which I subscribe, someone recently claimed success at grinding biochar with an ordinary electric leaf shredder. These devices may not shred leaves very well, he said, but as a biochar grinder, the one he used was fast and efficient. I had to know!

With the loan of a 14-amp chipper/shredder from a friend, I was grinding char down to about 2mm or less about twice as fast as my wooden grinder. Prior experience with an 8-HP gas-powered shredder had taught me to aim for 50% moisture by testing the char with a hand-held probe (wetter material clogs the machine; dryer char makes too much dust).

At 50% moisture, this 14A Portland 1-1/2” capacity chipper/shredder from Harbor Freight can make finely ground biochar all day. Wheelbarrow contains 1/4” charcoal made with hand-powered grinder.

The moisture meter I use, General MMD4E, is the one Kelpie Wilson uses to test whether brush and wood is dry enough to pyrolyze without making too much smoke. It measures the electrical resistance between two sharp probes, which are designed to be inserted into wood, but which seem to work just as well with a pile of biochar.

Making biochar in the woods can be an alternative to chipping, incineration, and lop-and-scatter. It will probably generate more biochar than you can use in your garden. The remainder can be flung around for the benefit of the forest without grinding or inoculation, because it will gradually be pulverized and charged as it’s absorbed by the soil along with the other litter.

The Complexity of Biochar Production

In the parable of The Five Blind Men and the Elephant, each man correctly describes the part he is touching, but is mistaken in applying his experience to the whole animal.

The circumstances within which biochar is made result in different choices for equipment, co-products, and overall scale. A centralized facility only pencils out where biomass can be economically delivered to a large stationary plant, and applications for the co-products of heat and electricity may be needed to make it do so. At the opposite end of the scale, in remote locations with no practical opportunities for making use of heat and electricity, making biochar is simply a superior alternative to chipping or burning and is done with mobile devices, compact kilns or no equipment at all.

A recent burn with the Vuthisa kiln. Heat is used here to perpetuate and improve pyrolysis, so it’s not really going to waste!

The product, biochar, is the same in all cases, with variations in quality. Those variations often matter in the market, but I would argue that they do not matter significantly in the soil. I disagree that making biochar should be combined with cooking, heating, or power generation as a rule. We are all making the same substance, but our needs are different.

I sympathize with anyone explaining biochar to novices, of which there are many, because I face the same problem with great regularity. Given the cheap availability and convenience of fossil energy and petroleum-based products over many decades, biochar and pyrolysis are simply not familiar to most people in our culture. How biochar production is done, and what you do with the biochar and its co-products, will vary according to which part of the proverbial elephant you are touching.

Not Your Grandfather's Biochar

Since the discovery of Amazonian terra preta soils in the 1950’s, biochar has been thought of as a soil amendment by Western culture. Seen through the lens of history, there is no other application for it, besides drinking water filtration and relieving gastronomic distress. As far as we know, that’s all that humans ever figured out to do with it.

The Ithaka Institute knows better. Published in 2012, their “55 Uses of Biochar” recognizes many more ways that biochar can improve our lives, relatively few of which involve soil. Careful and consistent attention to process conditions can produce a wide variety of precisely tuned materials for specific applications in a surprisingly diverse range of disciplines. The Ithaka article presaged many of these.

Take snowboarding for example. Who would have thought that biochar would turn up there? Ithaka did, at least in concept—in uses #31 (carbon fiber) and 32 (thermoplastics). The explanation entails quantum physics, but you can skip over that section and still get the point.

Maurizio Bormolini (center) rides biochar to victory in World Cup 2024/25

Granted, highly evolved chars are out of reach for the average bio-collier. But experience begets innovation, and the ambitions of younger biochar practitioners can be served by these advanced applications. Start where you are and see where it takes you.

As the snowboard article states, biochar has a durable value as a soil amendment in gardening, although not for industrial agriculture as it turns out. But all biochar placed in a static medium keeps carbon out of the air, regardless of sophistication. Fortunately for the world as we know it, the limits of carbon sequestration with biochar will probably continue expanding, through human ingenuity.

Biochar's Future

Biochar is usually described in terms of its applications and its value in carbon sequestration, based on its inherent qualities. In a fire-adapted landscape, making biochar also has a role in managing fuel—a service that fire itself normally provides. We make biochar from material that would otherwise burn in a landscape fire. To restore healthy fire in a landscape that has been deprived of it, we first have to reduce the accumulated fuel. We might as well make biochar from it. That way, we accomplish more than just fuel reduction.

Releasing a forest meadow from Douglas-fir encroachment and making biochar from the encroachers

Making biochar in a fire-adapted landscape is only tied to fuel reduction until the fuel is reduced. We have to reduce fuel to save the forest and ourselves. But if and when we ever catch up with the fire deficit, biochar will still be made for an abundance of practical reasons, and by then we will have discovered more of them.

Forests can be managed to supply vastly more biomass than we currently use to make biochar while restoring them to health and keeping them that way. We could increase soil carbon much faster, and given biochar's durability, it can be increased indefinitely. There is actually no limit to how much biochar we could make. Photosynthesis guarantees that.

This capacity will continue after we run out of fossil fuels. The energy density of fossil fuels will be hard to replicate, but as they become more expensive to extract, alternatives will increasingly pencil out. Biochar will gradually become more important as we learn to modify it to replace fossil energy sources. Most likely, biochar will become integral to our way of life. The future of careers in chemical engineering is assured by this, along with related industrial opportunities.

Many Roads to Biochar

Beyond the basics of what biochar is and what it can do, there is a wide frontier for its deployment. The way that biochar is made and used will vary from one situation to the next, depending on many factors. There is no universal template for a biochar system.

As an example, the Cook County, MN Highway Department, has an unusual mandate to help control invasive species, which were being propagated by their existing practices. So the department teamed up with the state ag inspector and an environmental technician to make biochar from them. Not only would the soil be improved on site and elsewhere in the county, but reestablishment and fuel loading would be largely eliminated.

The $10–20,000 equipment budget for their first two kilns suggests that a Big Box kiln design was chosen. Another municipality working at this scale (3,300 square miles) with greater revenue sources might have chosen a CharBoss, or even a TigerCat Carbonizer, which was used in the Oakland Hills to pyrolyze entire trees. Besides budget and scale, other factors influencing their choices would be the high accessibility of their highway right-of-ways and the fairly level terrain.

This set of factors is a far cry from the forested slopes and winding roads of western United States, where the approach tends toward using hand crews with Ring of Fire kilns and water trailers. In the vertiginous, largely undeveloped forest of southern Humboldt County where I live, a kiln that does not require water for quenching makes even more sense than a Ring of Fire, so I chose the air-quenched Vuthisa design. And wherever funds are sufficiently tight, biochar can be made in piles or pits with little more than your own time and sweat.

Workforce Training in Forest Health

making biochar as an approach to managing biomass

During the pole construction workshop in Whitethorn last September, it was hard to miss the enormous pile of debris across the driveway. We were erecting a shade structure at the native plant nursery at the Lost Coast Education Center in back of the Whitethorn BLM field office over the weekend. I knew that BLM stations in other states were making biochar, but not here. What a great opportunity for an exhibition!

The following Monday, I contacted BLM King Range National Conservation Area about making biochar from the pile. Kacie Hallahan put me in touch with Bryan Boatman, Fire Management Officer for BLM in Arcata, who liked the idea. He had been prepared to incinerate the pile, but he was curious about biochar.

I had just learned that the California Conservation Corps now owns one of Kelpie Wilson’s Ring of Fire kilns. Brian Starks at CCC Fortuna said yes to bringing a crew and the kiln to train them in making biochar. I put “the other Brian” in touch with Bryan Boatman, and the three of us chose Monday, Feb. 24 as the date. Bryan got someone to cover the pile with a tarp, but after it blew off in the big December storm, the pile never really dried out. I made sure we had propane torches on hand to light the kiln.

Bryan covered the pile as best he could.

The night before the presentation, the weather forecast was for rain and wind, so Bryan and I chose to switch it to Tuesday Feb. 25. The prediction for Tuesday was great.

This had no effect on Brian Starks and his CCC crew, who had committed to working Monday through Wednesday. The backhoe operator, Wayne from BLM, dismantled the pile for them and spread it out. Bryan Boatman and I were there to help. But even with two propane torches, it took over 1-1/2 hours to get this wet brush to light.

We worked all day in the rain, and it took three days for my boots to dry out!

At the end of the day on Monday, the CCC crew staged brush a for Tuesday’s burn and left a nice ring of biochar. The green grass and unburned leaves under the biochar impressed BLM engine operator Angus, who had seen many burn scars from pile burning. This is one of the chief benefits of switching from incineration to making biochar.

Small results from wet brush, but no soil damage from the burn. Dismantled Ring of Fire and covered pile for conservation burn in background.

Tuesday dawned warm and foggy, then became bright and sunny. The C’s got right to work scooping up the biochar, then setting up and loading the kiln again, with help from Wayne and his backhoe.

Wayne sifts through eight years of debris. Painted wood, PT and plywood are set aside to exclude contaminants from the char.

At about 10:15, we had about a dozen guests who came for the presentation. I addressed the group for 45 minutes or so and answered questions.

Talkin’ char with the assembled guests. If the tumbler on the tailgate is yours, contact me!

By the end of Wednesday, the brush pile was consumed, and LCEC ended up with a couple of cubic yards of biochar. How much carbon was displaced from the atmosphere? Check out my earlier post, How Much Carbon Does Biochar Sequester?

California Recognizes Cultural Burning

Last month, the State of California officially recognized the right of first peoples in the state to practice burning the way their ancestors did. Senate Bill 310, which passed the state assembly and state senate in September, has been entered into law and is in effect as of February 27.

The new law restores tribal sovereignty to the 109 federally recognized tribes in California for the use of Traditional Ecological Knowledge of fire in their ancestral territories, allowing them to burn without state permits, and places tribes on equal footing with the California Natural Resources Agency and local air resources control boards. Tribes can also access the Prescribed Fire and Cultural Burning Claims fund without having to complete formal burn plans.

Tribes use fire to enhance food sources, fiber resources, and medicinal plants as part of their belief system, while also establishing and maintaining wildfire resilience. This layered practice distinguishes cultural burning from prescribed burning, which simply reduces the severity of landscape fire. Together they are referred to as healthy fire.

Healthy fire and biochar both reduce fuel in overstocked forests that has resulted from over 100 years of fire suppression. They can be seen as bookends, approaching the wildfire problem from opposite directions. Where manual fuel reduction is unnecessary, fire can be returned to a unit of forest land in a single step. Otherwise, manual treatment comes first, and the thinned material can be pyrolyzed and left in place as biochar, a valuable soil amendment for long-term forest health. In either case, the endpoint is to manage land with fire. Making biochar can be seen as transitional toward that end, although some will continue to be needed by us indefinitely.

We can be grateful that TEK still exists in California and that tribes are willing to work with us after all the damage that our culture caused to the forest and the people who sustained it before we arrived.

A press release from CNRA is available here.

The Soil's the Limit on Adding Biochar

How much biochar should you add to your soil? The answer hinges on an understanding of biochar.

Sand, clay and silt consist of minerals. They provide a substrate for the formation of organic complexes, which bind the soil particles. Very slow weathering and dissolution by microbes can bring minerals into circulation in the soil food web. Biochar is not a mineral, but it behaves the same way. Like minerals, it is inert in the soil. However, it has a vastly greater surface-to-volume ratio. This is what supercharges soil life and productivity.

Biochar does not directly enhance soil productivity. Its tremendous contribution to soil ecology is indirect, through increasing the surface area required by the organic complexes that constitute soil life.

Our recent trials indicate that biochars that are engineered to build soil carbon and placed in the rhizosphere and … applied every year … can build an extra 1 tonne of carbon in 1-2 years. Suggest you read Han Weng's work on this which we summarised in Joseph et al. (2021), How biochar works, and when it doesn't: A review of mechanisms controlling soil and plant responses to biochar.

– Stephen Joseph PhD, Renewable Energy and Biochar Researcher and Consultant, UNSW

Any char is good. Some are better. Cooking at above 450°C provides permanence. Below that more SOC (food) but less biochar (structure).

– Albert Bates, coauthor of Burn and Terra Preta

Low temperature biochars can have a long lifetime if they form an organomineral coating on their surface and are taken into the soil microaggregate structure.  This often occurs quickly in many tropical and sub tropical soils that have a high clay content.

– Stephen Joseph

How much is enough? The limit depends on whether labile organic matter (food) and water are in good supply. You will read that diminishing returns and possibly even lower yields start above 10% biochar by volume in the root zone. This may be because mineral availability begins to become limiting above that percentage. However, the exact level will probably depend on your mineral soil structure, so your mileage might vary accordingly. Best to conduct experiments in your own garden.