Carbon sequestration: agriculture

Agriculture holds enormous opportunity to provide solutions to climate change, one of these solutions is carbon sequestration, which is the absorption of carbon from the atmosphere into soils and vegetation.

Plants and soils both have the potential to accumulate carbon and store it if managed properly. Farmers therefore manage thousands of tonnes of carbon on the nation’s behalf – with the potential to help themselves and the planet to reach net zero. Soil management, hedgerows, and trees both in fields and in woodland can all count towards this.

Accounting for this sequestration, however, can be difficult. Additionally, as these are all complex biological systems, there is often wide variation in results. Nevertheless, we have put some examples below.

According to the Natural England report “Carbon Storage and Sequestration by Habitat: a review of the evidence” (2021), studies have found that:

• Arable/cultivated soils contained 27.5-88.2 tonnes of C per ha in the top 30cm (not including deep peat soils)
• Improved grassland soils contained 72-204 tonnes of C per ha in the top 30cm (not including deep peat soils)
• Soils under arable land use were net emitting CO₂ on average, while improved grasslands net absorbed CO₂ on average (but not always). Both arable and grassland on deep peat soils emitted larger amounts of CO₂

However, confidence in these figures was rated low to medium. This is because figures often come from only a few studies or one study, with a wide range of results. Data is from tables 3.1 and 3.2.

According to the Natural England report “Carbon Storage and Sequestration by Habitat: a review of the evidence” (2021), studies have found that:

• A minimally or unmanaged hedgerow stores 45.8 tonnes of C per ha in its vegetation, ±12.3t
• A 30-year mixed broadleaf native woodland on mineral soil stores 114 tonnes of C per ha in its vegetation, range 22-204t
• Additional carbon is also stored in the soil under this vegetation

However, confidence in these figures was rated low to medium. This is because figures often come from only a few studies or one study, with a wide range of results. Data is from tables 2.1 and 2.8.

To increase carbon removals or sequestration, farmers can look to:

• Improve and increase vegetation on marginal farmland such as hedgerows, meadows and wildflowers, and trees
• Improve soil health which can be achieved with improved soil management, through soil testing and developing and following a soil management plan using GREATsoils and RB209
• Change land use or management

It should be noted that when calculating your own farm’s sequestration, particularly for soil, calculators often use international averages (Tier 1 factors) which may not be fully representative of your soil. AHDB is calling for an improvement in this data to baseline and better represent UK soils.