A farmer’s guide to soil carbon

Interest in soil carbon has been growing, but quantifying it has been something of a mystery for farmers. The Soil Carbon Project set out to change that, says Alex Bebbington, Project Officer for the Rural Business School.

The idea for the project came from Farm Carbon Toolkit, which approached AgriTech Cornwall for help in finding the best scientifically-based yet practical testing methods for farmers. The project was launched in 2018 as a collaboration between Duchy College’s Rural Business School, Plymouth University, Rothamsted Research and Farm Carbon Toolkit.

Simplifying soil testing

Over three years, soil samples were taken from more than 400 fields from 83 farms across Cornwall and Devon, explains Alex. Various simple ‘in field’ tests were carried out on the samples to investigate worm counts, water infiltration rates and aggregate stability.

“The samples were also sent away for analysis so we could explore links between soil carbon results and the tests farmers can do themselves in the field,” he says.

“We found aggregate stability had the strongest relationship with soil carbon. It meant that by doing a simple aggregate stability test, farmers would have a very good indication of the quantity of carbon in their soil and the ability to compare it over time.

“Carbon holds soil together. Soil holding its form contains a lot more carbon than one that falls apart easily. It also means you won’t lose half the field out of the gate when it rains!”

It was easy to engage farmers with the project, he continues. “They came to us. Farmers are interested and know soil carbon is important. They also appreciated the project was giving them evidence to back up what they were doing.”

The project team produced a field and lab guide in October 2021 which summarises how to take a soil sample and how to perform the test. It can be read online or downloaded here.

What’s next?

The project’s findings led onto a new project: Farm Net Zero. This builds on the findings and seeks to help Cornwall’s agricultural industry better understand how soil carbon can help farming businesses achieve net zero.