All About Biochar: An Eco-Friendly Burn

by | Nov 8, 2024 | Resources

Biochar is a preferred alternative to pile burning for vegetation management because it reduces smoke (and carbon emissions), increases soil and forest health, and reduces scarring on the forest floor. The best part is that it’s an easy modification to traditional pile burns!

What is Biochar?

Bio-charcoal (Biochar) is the nearly pure carbon residue leftover after pyrolyzing woody biomass.  Pyrolyzing is a fancy term that basically means cooking wood (or other biomass) in a low oxygen environment to burn off the volatile compounds and other gases. The result is similar to the charcoal briquets that you’d buy at the store for grilling.

Biochar is an Ancient Technology

Native Americans have been using fire to cultivate the landscapes in Sonoma County for thousands of years. In fact, indigenous peoples in both North and South America have used fire to cultivate crops, create natural fibers for baskets and clothing, and increase forage for game since time immemorial.

In the Amazon River basin, terra preta (translation: black soil) has been found widely distributed near pre-Columbian settlements and, to this day ~450 years after these settlements disappeared, terra preta soils are much more fertile than other Amazonian soils, which are otherwise naturally poor.

Historically, charcoal created by low intensity fires in our region was a key component to the fire-adapted plant species and increased nutrient cycling in the soil, but it has declined due to fire exclusion and suppression.

Why Char Instead of Burning?

Creating charcoal from woody plant debris rather than burning it to ash has a number of benefits:

  1. Less smoke and up to half the carbon emissions – In the biochar method, the gases and volatile organic compounds (VoCs) released by the biomass as it heats up are consumed by flames and burn far more cleanly than in traditional, bottom-lit pile burning.  It also minimizes scarring on the land from pile burns, which burn hot close to the ground.
  2. Increases soil fertility – The exact mechanism is still being worked out, but soils with biochar increase soil cation by up to 30%. That’s a fancy way of saying it makes more soil nutrients available to plants.  Microbes colonize the porous structure of the biochar and use the negative ions in the biochar to increase their metabolic rate and provide more minerals to plants.
  3. Increases water retention in the soil – Biochar’s porosity also soaks up water during rains and then slowly releases it over time. This reduces erosion and runoff and also acts as a “water bank” for plants and crops growing in those soils, which further increases drought tolerance.

How Do I Make Biochar?

To create bio-charcoal instead of ash, you simply need to make a few modifications to your normal pile burn:

  1. Wait until it is safe and legal to burn, typically November to April.
  2. Stack the biomass in a clear area away from structures and overhanging trees.
  3. Secure sufficient water for dousing the flames, typically one gallon per cubic foot of biomass.
  4. Biomass of similar size is best: typically no thicker than four inches in diameter and no longer than 4 feet in length. The smallest recommended size is about 3×3”. The biomass should be dried for at least a few weeks after clearance.
  5. Pile the biomass up to 4 feet in height and 4 feet in diameter like you would stack a normal pile burn.
  6. This next step is key! Light the pile from the top. Feel free to use a fire starter to assist.  By lighting from the top, the hydrocarbon and volatile gases in the wood are consumed by the flames, which reduces smoke and pollutants and results in a cooler, more controlled burn.
  7. Monitor the pile while it’s burning.
  8. Periodically add more material, as the fire allows.
  9. When the pile is reduced to coals, but before it turns to fine ash, rake them out and douse with water until the coals are cold. Think of how you rake out a campfire before going to bed; you want to be able to pick up the biochar in your hand.

You can also contact Raymond Baltar with Sonoma Ecology Center with questions, rent one of their Ring of Fire biochar kilns, or request resources and assistance.

Biochar reduces the volume of biomass by about 90%.

What Do I Do With Biochar?

If you want to use the biochar for agricultural applications or in a garden, collect the biochar and mix into compost.  Recipes we’ve seen range from 1:10 or 1:2 ratio of biochar:compost depending on the pH of your soil (biochar is alkalizing).  

You can also soak in compost tea.  For best results, let the biochar+compost or tea mixture cure for two weeks and then incorporate into your soil.  

Biochar is a sponge for moisture and microbes, and you want it to absorb nutrients in a compost pile before incorporating into agricultural soils.

If you’re applying back into a wooded area with established trees, broadcasting the biochar over a wide area is fine.  The goal is to avoid concentrating too much in any area.  This mimics historical low intensity fire.

Learning More

Here are some resources if you’d like to learn more: