David Yarrow ponders a question at the workshop.
On a beautiful sunny weekend recently I attended a 2-day workshop presented by David Yarrow on making and using biochar. It was at a local farm, there were 20 or so attendees, and the workshop involved us making a burner out of a recycled 55-gallon barrel, burning biomass in it to create char, and then making a growing bed using the char as well as David’s favorite minerals, activators, and inoculants for it.
Here is presenter David Yarrow, showing us the materials we will use to make the burner. They include a barrel with removable lid, some stovepipe pieces, a roll of ceramic insulation, a roll of chicken wire fencing, some wire and hardware. Tools needed were a power drill and disk grinder, a metal saw, and various hand tools.
I took photos throughout the workshop, and print some of them here in chronological order, along with notes about the photos and the information we gleaned at that part of the presentation.
Biochar is charcoal that is made by particular methods to yield carbon for effective use in soil. David presented from his experience on how to activate raw biochar with various minerals and inoculants, and also showed how biochar can then be put into a raised “lasagna” bed with biomass and other materials to make fully fertile soil.
David teaches how to use a TLUD (Top-Lit Up-Draft) burner to make biochar. A TLUD is a two-stage device with a biomass gasifier in a 55-gallon barrel, and a secondary gas flare in the chimney. It is smokeless, cheap and easy to make, and reliable. It makes small 15 to 20 gallons batches for test plots.
The other major way for making biochar is by pyrolysis – burning it in the absence of oxygen in a sealed chamber called a “retort.” Like a baking oven, a retort is closed so air can’t enter. Heat is applied to the outside or bottom and the biomass inside chars (or “carbonizes”) without catching fire and burning. Larger commercial burners usually involve retorts because they are more efficient at converting more of the biomass to char — up to 50%. Retort & kiln pyrolysis also allows the capture of gas, vapor and liquid by-products that can be processed into biofuels to replace fossil fuels.
The TLUD we are making is a much simpler and less dangerous design than one involving a retort. In this design the biomass itself is burned, but with limited oxygen allowed to enter. At the end of the burn, most of the biomass will have been oxidized, but 20 to 30% of biomass carbon will remain as char.
Here we cut vents into the reducing thimble to allow air to enter it. The thimble is a crucial element of the design, creating a venturi effect when the hot gases leave the drum and enter the thimble. These gases must be burned in the stovepipe for the combustion to work properly.
The top of the drum is removed and a 6” diameter hole cut into it. Then an 8” to 6” stovepipe reducing thimble is inserted from the top.
Once vents are cut into the thimble, they are pressed open to admit air. Again, the exact amount is something that you must play with. As with the holes in the bottom of the barrel, too little air and the burn goes smoky, too much air and you burn up most of the char.
For the next burn, David will open the thimble vents wider and add more holes in the barrel bottom to get more air in for a hotter smokeless burn, and will shut the burn off sooner.
We run the biochar through a ½ inch screen. The smaller parts will be used in the planting bed, the larger ones returned to the next burn.
To keep the internal temperature high during the burn the drum is insulated. A piece of poultry wire fencing is laid out, a section of 1” thick insulation is laid on top, and the drum is rolled onto this. The ends of the chicken wire are then pulled tight and wired together, holding the insulating jacket on the drum.
3 guy wires secure the chimney in case of high winds
A piece of 8” diameter stove pipe is where the flammable gases given off from the smoldering biomass in the barrel will burn. It is inserted into the 8” end of the (now vented) thimble in the top of the drum. Guy wires are attached to hold the pipe vertical in a wind.
We start filling the drum. The most important thing is that the biomass be fully dry, to minimize steam and assure a hot burn. Virtually any biomass can be made into char – wood, hay, manure, bones. Very small stuff (sawdust and leaves) don’t burn well in a TLUD because it will not pull air very well up through the contents of the drum. Very large woody chunks (3” thick logs) will not char totally in the fast burn this device creates.
Now the barrel is filled and ready to be lit and the lid and chimney put on.
The fire is lit. This can be done many ways. A little paper under a top layer of kindling works well. An accelerant like kerosene can be used, but for purists is cheating. The fire needs to burn to the state of having bright, glowing red embers before the lid and chimney–top is put on, because closing it will drastically reduce the presence of oxygen. From now on until the end of the burn, fresh air must be sucked up from the holes in the bottom of the barrel.
During a good burn the fire is visible through the slots in the venturi.
David checks the burn by peeking under the lid. White smoke coming out the chimney means that the fire in the barrel is not hot enough yet to ignite and sustain the gas flare in the chimney. More burning needs to happen in the barrel.
Once the burn seems well established the rest of the chimney is added before it gets too hot.
David checks the progress of the burn again. Now the burn is going well. Little smoke is coming out and you can hear the intake of air swooshing in the slots cut in the chimney adapter, The drum is set up on three short cinder blocks to provide stability and room for air to enter under it.
Volatile gases are being boiled out and driven from the biomass by the heat inside the barrel. When the hot gases enter this vented thimble they ignite and burn in the chimney. Once the barrel burn is established, if the gas flare combustion in the chimney goes out (which you know immediately because all of a sudden the chimney will smoke), it can be easily reignited with a match or lit piece of paper being inserted into one of these vents.
In the middle of a good burn there is no smoke visible at all, yet you can see the flames through the thimble vents.
The burn is ended with water from hose.
The burn is finished. The signal for that is when embers begin to drop down through the bottom air holes. That means the burn, which started at the top, is now reaching the bottom. David carefully removes the cinder blocks to lower the barrel onto the ground and restrict air being sucked into the barrel bottom. The last bits of biomass on the bottom may continue to burn a few more minutes Smoke changing from woody fragrance to stinky means charcoal is now burning to ash—time to extinguish the fire.
Water is sprayed into the barrel with a hose to kill the remaining fire and embers. A charcoal fire in the barrel bottom is very hot, very stubborn, and very hard to put out. It helps to have an extra lid to tightly close the barrel top and hold in steam. Apply a water spray at 3 minute intervals until steam subsides.
For the next burn, David will open the thimble vents wider and add more holes in the barrel bottom to get more air in for a hotter smokeless burn, and will shut the burn off sooner.
We run the biochar through a ½ inch screen. The smaller parts will be used in the planting bed, the larger ones returned to the next burn.
Making the Garden Bed
After the wood chips we add a thin layer of leaves, then straw and then cover that with a thin sprinkling of compost and/or manure. Compost and manure serve more as an inoculant for digestive microbes than a major nutrient source.
We are making a planting garden bed perhaps 4’ wide by about 10’ long . David uses a “lasagna” or “sheet layering” style, adding thin layers of various materials that will allow microbes and minerals to blend rapidly together. He starts with a layer of sticks and coarse, rotten woody debris right on the ground. This will provide plenty of air spaces at the base, as well as a substrate guaranteed to attract and feed fungi. Here, the layer of sticks is in place and we are covering it with wood chips.
After the compost layer goes the first layer of screened biochar.
After the biochar, David adds a thin scattering of dried sea minerals. They add the full menu of trace minerals that are in sea water.
After the light-colored sea minerals, David likes to add rock dusts to feed the microbes.
First cover of char goes on after compost copy
Much to David’s dismay (he considers calcium the basis of good growing) we did not have any limestone, gypsum or other calcium source, so the workshop host, Marty, adds some liquid calcium-magnesium he had, mixed with water.
David often uses SumaGrow, a microbial inoculant that he knows is effective. Here it is sprayed onto the biochar and minerals as the next layer after the Calcium-Magnesium blend. It features 16 bacteria and 9 fungi in a 12% humate solution to perform their microbial wonders with the crops to be planted.
Another layer of straw goes on after the inoculant spray.
Marty blended a teaspoon of mycorrhizal fungi spores in a pint of very fine biochar dust to bulk the tiny spores up in volume, then scatters the dust onto the bed after the whole thing is inoculated.
Marty then shakes fine biochar dust that David saved from previous burns onto the bed after the whole thing is inoculated.
Topsoil from a horse farm is lightly scattered on after the fine char dust and fungal spores. This seals the first stack of layers that forms the base of the new bed. Next comes a second stack of layers that create a primary root zone for seeds and seedlings.
Next, green weeds are laid on the bed to assure an abundance of bacteria food and jumpstart the fermenting digestion. Green, juicy plant debris also supply some nitrogen.
High-carbon wood shavings are the first layer of the second stack of layers. This is followed by a layer of lighter weedy biomass such as hay or straw. Old moldy biomass is best for a bed.
Now a layer of rotting apples is applied to bring local fungi and bacteria to the pile and provide a sweet treat for the microbes.
Next Marty adds a layer of rotted hay. Leaf mold gathered from a nearby woodland is next, to bring a wide diversity of indigenous fungi, and even other bacteria and microbes to the bed.
A few more sea minerals are added to boost trace elements in biomass layers of the second stack. Sea minerals are 100% soluble trace elements, and very alkaline, so only a thin sprinkling of trace elements is needed — one cup to one pint on 100 square feet.
Another layer of biochar — in this case a fine powder blended with mycorrhizal spores — can further enhance movement of minerals and microbes. Biochar adsorbs nutrient ions and electrons and keeps these charges available in the root zone. So biochar is like a battery to hold electric charges in soil, and release them to grow plants. Thus several thin layers of biochar, rather than one thick layer, create far greater surface area and charge capture capacity — a bigger battery in the soil.
Finally we add another thin layer of sprinkled soil to cover the biomass and microbes inside, then a loose layer of straw mulch to shade and shelter this microbial mega-metropolis, ending with a good soaking with well water. Water is the trigger to activate and mobilize minerals and microbes.
David says this thinly-layered, well-aerated bed can be planted in a week (unless overloaded with manure or green matter) by depositing a strip of soil on the thin mulch, and seeding into this furrow. Transplants just need a hole opened easily by fingers, dropping in the plant and root plug, and gently pulling the soil up close (be sure your transplants get 5% biochar powder in their potting mix). Roots penetrate quickly, find what they need.
One more layer of compost, then straw, and finally a good soaking.
Fungi grow quickly, find what they need. Then roots and fungi get together and the explosion of growth begins. It seems to take 30 days for this symbiosis to get into high gear, and it takes a full year for earthworms to move their families in and do their work.
Over winter, a new bed will shrink to 50% of its volume, but underneath, soil microbes are kept fed, sheltered and warm enough to continue digestion and growth. Do not disturb them with any tillage or other soil intrusion. Annual maintenance is simple—add a new stack of layers, usually in fall, to mimic how Nature builds soil by recycling layers of biomass, dust and enrichments (like migrating herds or fire). After this initial loading, a well-made lasagna bed stays fertile and productive for many years, but much lighter annual doses of minerals can be added. Rock minerals digest slowly, and deliver a long-term fertility that easily lasts a decade—longer if intelligently managed. Just a few lasagna beds are so productive they easily (in every sense) deliver enough vegetables for a large family.
The workshop concludes with participants surveying their work. The burner we made, to the right, produced the char we screened and applied to the bed we built in the center rear.
