Charcoal

Is charcoal allowed as a soil amendment in organic farming?

The answer depends on how the charcoal is made. If the charcoal is produced by burning untreated plants or animals, then the charcoal would be permitted as a soil amendment on organic farms. Guidance NOP 5034-1, Materials for Organic Crop Production lists biochar as an allowed nonsynthetic substance. Charcoal produced by burning manure, sewage sludge or fossil fuel sources, such as coal, is prohibited.

Fly ash (the residue from coal furnaces) is also prohibited as a soil input. The NOP rule also prohibits burning as a means of disposal of crop residues, unless the burning is used to suppress the spread of disease or to stimulate seed germination (7 CFR 205.203(e)(3)). Therefore, any burning of crop residues would need to be documented in the Organic System Plan consistent with those purposes and approved by the organic certifier.

What is ‘biochar’ and what can it do for my soils?

A growing number of charcoal products are claiming to be ‘biochar’ or ‘terra preta,’ which are specific forms of charcoal produced by pyrolysis in reduced (low oxygen) conditions. The soil organic matter is supposed to be more stable as a result. However, researchers have found mixed results. For example, some researchers have found that biochar may not be useful in well-drained and clay soils. Other researchers have found that biochar can be useful in marginal soils with high acidity, such as found in abandoned mines. Biochar can be made from many materials and processes, yielding different characteristics. Biochar is also applied at a variety of rates. These factors make evaluating biochar more complicated.

In theory, the process withdraws atmospheric carbon dioxide and stores it in the soil, potentially serving to reduce carbon emissions from agriculture. Proponents claim that wide spread use of the material may help prevent climate change. However, evidence is not clear about the effects of biochar on net carbon emissions. Techniques to sequester more carbon in the soil may be offset by what is released during its production and subsequent effects on soil decomposition processes. Just as biochar has different effects on soil fertility depending on soil type, its effects on carbon and nitrogen emissions in soil vary with soil type and different latitudes.

Revised and updated in August 2023 by OMRI Research and Education Manager, Peter Bungum. This article was originally published in the Spring 2009 Newsletter by Brian Baker.