Farmers in England will bury burnt wood in fields to capture CO2

A large trial is underway to see how much CO2 can be removed from the atmosphere by burying a charcoal-like material in fields

By Adam Vaughan

Farmers in England are starting to bury a charcoal-like material in their fields to see if it could offer a new large-scale way of putting the brakes on climate change.

Biochar is the carbon-rich material left over from burning wood and other biomass at high temperatures in an oxygen-free environment. Most of its use today is at the small scale, such as gardeners using it as a fertiliser.

However, a team led by Colin Snape at the University of Nottingham, UK, has started burying up to 200 tonnes of biochar in fields to gauge if it could help meet the UK’s net-zero goal by removing millions of tonnes of carbond dioxide from the atmosphere. It is the biggest biochar trial yet in the UK, and one of several CO2 removal ideas in a £31.5 million research programme, including scattering rock dust on fields and planting more trees.

“The key thing is that all of these greenhouse gas removal technologies, we need to test their viability. We need to figure out how big a slice of the pie biochar is. It’s about not putting all our eggs into one basket, of one magical technology that will save us,” says Genevieve Hodgins, who is managing the biochar project.

Around 15 tonnes of biochar is in the ground already, and more farmers are being recruited across the Midlands region of England this spring and summer to begin widespread burials this autumn. Beyond tackling climate change, a big attraction for farmers is that research indicates biochar can improve soil health, which is in a parlous state in England.

The project will measure how soil health changes over time, including the health of earthworms, as well how it affects crop yield and crop health compared with control plots. Some of the biochar will also be buried on land where tree-planting is planned, in order to see how it affects tree growth. Because the forested areas aren’t used to produce food for human consumption, far more biochar can be put in the ground there: Snape estimates about 50 to 100 tonnes per hectare compared with 10 tonnes for arable land.

Snape says that if the idea were scaled up for widespread deployment across the UK, the biochar would preferably be made from dried-out food waste and waste products from sawmills. However, to ease regulatory approvals by the UK Environment Agency for their trials, the researchers are using biochar made from virgin wood for now, mostly from one producer in Derby.

For the purposes of locking away carbon, that virgin wood would ideally have other uses, such as making timber-framed buildings, which the UK government’s climate advisers say should become more prevalent. Hodgins is looking at alternatives for making biochar, including coconut husks from Germany.

The project should give us a better idea of just how much CO2 biochar can remove. Snape thinks the approach could one day store a “few million” of the 130 million tonnes a year that the Royal Society calculates will need to be removed by 2050. First results may come in autumn 2023, potentially offering new insights into how permanent the removals are by showing how much microbes degrade the biochar.

Ultimately, Snape thinks biochar will be a minor player in the big picture of an emerging suite of ways to remove CO2. But he says it is ready here and now and it doesn’t require huge new infrastructure, such as the pipelines and underground reservoirs to store greenhouse gas in other suggested initiatives. Moreover, he say it is easy for the public to understand. “It’s something that looks like coal going back into the ground. People understand that coal, oil and gas came out of the ground and created the state we’re in today.”