Current approaches to measuring soil carbon may be significantly underestimating the amount of carbon stored in agricultural soils, according to early findings from a large-scale environmental baselining project led by AHDB. The results raise important questions about how soil carbon is assessed, valued and incorporated into future environmental and carbon accounting schemes.
The Environment Baselining Pilot, involving 178 farms across England, Scotland and Wales, has found that 30% or more of soil organic carbon on participating farms may lie below the commonly sampled depth of 30 cm. Researchers suggest this means many existing measurement methodologies could be missing a substantial proportion of total soil carbon stocks.
The project, supported by Quality Meat Scotland (QMS) and Hybu Cig Cymru – Meat Promotion Wales (HCC), represents one of the most comprehensive assessments of carbon stocks on British farmland in recent decades. More than 53,000 soil cores have been collected from over 5,000 fields, with sampling extending to depths of up to one metre where conditions allowed. LiDAR surveys have also been used to quantify carbon stored in above-ground features such as trees and hedgerows.
Initial analysis from the first 170 farms shows that approximately 95% of total farm carbon stocks are held within soils, with only a small proportion stored in woody vegetation. Across the farms assessed so far, average soil carbon stocks are estimated at around 128 tonnes per hectare, although substantial variation has been recorded between locations and soil types.
Some of the highest carbon stocks were found in deep organic soils in the Cambridgeshire Fens and Somerset Levels, where individual fields exceeded 600 tonnes of carbon per hectare. These findings underline the importance of soil type when evaluating carbon sequestration potential and environmental performance.
For soil scientists and land managers, one of the most significant outcomes is the indication that deeper soil horizons may play a much larger role in carbon storage than is often reflected in standard sampling protocols. If confirmed through further analysis, the findings could have implications for carbon auditing, ecosystem service payments and emerging carbon markets that rely on accurate quantification of soil carbon stocks.
Alongside soil sampling, participating farms completed carbon audits to estimate greenhouse gas emissions and removals. AHDB says the next phase of the project will investigate how factors such as soil type, land use, cropping systems and management practices influence carbon storage and distribution within the soil profile.
The project has also established a Scientific and Technical Advisory Group to help guide interpretation of the data and ensure outputs are scientifically robust. Further results are expected as analysis continues and additional farms are incorporated into the programme.
As interest in soil carbon continues to grow among policymakers, farmers and carbon market participants, the pilot highlights a fundamental issue for the sector: accurate carbon accounting depends not only on how much carbon is present, but also on how deeply we choose to measure.
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