Biochar

Making Biochar: Biochar is made using a process called pyrolysis. Here, that means charing at high heat in the absence of oxygen. Oxygen is then re-introduced in an after-burner to burn the volatile gases, smoke and soot–at the same time increasing air flow via the chimney effect. Since the oxygen is consumed in the initial burn, there is not enough oxygen left above the burn line to turn the charred material into ash. Once the burn is complete, the container is either sealed or drenched with water to stop the material from smoldering into ash.

1. Tiny scale in a single tin can: so simple, really no excuses not to try it.

2. Small scale in a gallon paint can, handout from Wae Nelson

3. Small scale using a wood stove (13 min) – EdibleAcres: make biochar while heating and cooking.

4. Large personal-scale operation (15 min) – John Rogers in Melbourne using 4 sets of 55 gallon drums. You could also use 30 gallon or 5 gallon metal containers.

5. Biochar workshop in 5 parts (about 40 minutes each) scaling up, using the energy generated from the process and minimizing the emissions.

6. New biochar production facility Living Web Farms creating biochar for their farm in Florida, refining the above workshop design, capturing excess energy for use in the greenhouse and drying, separating volatiles for use on the farm; experimental continuous-feed machine.

How much do you get? About 50% of the biomass turns into biochar, about 10% is required to create the charcoal, and about 40% can be re-captured as energy if your setup allows. That translates to about 1/4 of the original biomass in volume. The rest is water and volatile gases that are burned off.

Charcoal vs Briquettes Biochar is NOT the same as charcoal used in a backyard cooking grill. Briquettes are a chemical mix with many unknown additives; I wouldn’t even save the ash for the garden.

Natural charcoal is available for use in the grill, but I have found some brands are extremely hard with large chunks more like coal, that do not easily break up into suitably small pieces even with a hammer.

Charging Biochar: If you add raw biochar directly to a garden you could lose a season’s productivity, because it will absorb water and nutrients from the soil, robbing them from your plants. So before applying it to the soil, it is best to “charge” biochar for several days or weeks with water and nutrients (compost or worm tea, fish emulsion, urine, manure). Alternatively, mix it in while making compost, or add it in the off-season up north or if you leave a garden bed fallow. Once charged, biochar will continue to capture water and nutrients before they wash away.

Quantity to use in soil: 1-2 cups per square foot of soil minimum, 5-15% by volume of the top 6″ of soil is ideal. That would be from 1–2 cubic feet of biochar for a 4′ x 8′ bed mixed into at least the top 6″ of soil. Once applied, it is very stable; unlike compost or mulch, it does not break down over time.

Biochar can be applied under a layer of mulch for existing plantings; mixed with the soil more deeply for newly planted trees or planting beds; placed in a trench outside the drip line of a larger tree; or broadcast over a field. It can also be mixed in while making compost and later used as side dressing. Over time, worms will mix it deeper into the soil.

Summary: Biochar has many benefits. It provides a boost to soil microorganisms which improves the life, vitality and texture of the soil. It also improves the ability of the soil to absorb and hold water and nutrients, keeping them available to the plants over time while reducing runoff and down stream pollution. And it can help reduce greenhouse gases by creating a stable form of carbon that will remain in the soil for centuries.

Also be sure to check the “Building Soil” page under the Resources Menu.

By the way, char can be quite useful when you go camping. Create Char-cloth.