Biochar can help farmers reach net-zero greenhouse gas emissions. This carbon sequestration technology is particularly successful in reducing nitrous oxide emissions.

A recent review of more than 200 field-based studies worldwide examined the impact of nature-based carbon sequestration technology on agricultural emissions. The results were promising.

Biochar produced from organic waste is particularly “successful” in reducing nitrous oxide emissions, researchers from Ohio State University (USA) have found. The study, published in the scientific journal Journal of Environmental Quality, also highlights other benefits of biochar, including its ability to optimise soil.

The authors hope their research will help promote the commercial use and adoption of biochar in agriculture and forestry.

According to data from Our World in Data, agriculture, forestry, and land use generate more than 18% of global greenhouse gas emissions, 3.5% of which is related to crop burning.

What is biochar?

Biochar is formed by heating biomass, such as fallen tree branches and crop residues, at temperatures of 200-400 °C with little or no oxygen, through a process called pyrolysis.

In pyrolysis, organic waste decomposes thermally into a solid carbon residue, also known as biochar. Storing carbon in a stable solid form prevents it from decomposing. It can be stored in the soil for hundreds or thousands of years.

If farmers leave crop residues in the field to decompose, only about 10-20% of the carbon in the residues returns to the soil. By processing plant residues into biochar and incorporating them into the soil (the field), about 50% of the carbon is stored in a stable form.

This process reduces emissions caused by organic waste that is burned or left to decompose, as both cases generate greenhouse gases.

By using biochar, plants also absorb greenhouse gases directly from the atmosphere. Furthermore, it can be used as a soil amendment to improve drainage, aeration, plant health, crop quality, as well as water and nutrient retention.

How effective is the impact of biochar on reducing emissions from agriculture?

Nitrous oxide, methane, and carbon dioxide are heat-trapping gases that cause the Earth's atmosphere to warm.

The study found that by reducing emissions at their source while simultaneously enhancing carbon sinks that absorb them—in this case, soil carbon storage—farmers can achieve net-zero or negative emissions.

The researchers found that the use of biochar reduced nitrous oxide emissions by an average of about 18% and methane by 3%.

Although biochar alone was not effective in reducing carbon dioxide emissions, it helped when combined with commercial nitrogen fertilisers or organic materials such as manure or compost.

Biochar also has the potential to reduce greenhouse gas emissions from the soil, but longer studies are needed to verify this, the report notes.

What are the barriers to the adoption of biochar?

Currently, biochar is expensive – its price is €930-3065/t.

There is also insufficient evidence of its benefits and stability, due to a lack of large-scale long-term studies. Therefore, it has not yet been recognised as a carbon offset method.

However, biochar’s ability to sequester large amounts of greenhouse gases, as well as its additional benefits to farmers, means it should be re-evaluated as a tool for climate change mitigation, the study authors argue.

“If we can convince farmers that turning biomass into biochar is good for the long-term sustainability of the soil, the economy, and the environment, then we can achieve widespread adoption of this technology,” says lead author Raj Shrestha (Raj Shrestha).