Increasing the amount of carbon in UK soils will be key to achieving the farming industry’s goal of accomplishing net zero by 2040, with recent data identifying that 5 MtCO2e/year could be stored in soil.
For this to work in practice, farmers need to know the capacity of their soil to store carbon and how management practices can be used for different soils types to enhance soil organic carbon, while ensuring future profitability.
Kingshay Independent Dairy Specialists have recently released a report on soil organic carbon (SOC), which shows how farmers can measure, increase and monitor levels of carbon stored in soil under grassland.
Kingshay’s Sarah Bolt, author of the report, explains soil samples from 100 farms in England, Wales and Scotland, combined with farm and field profile information, were used to further knowledge of the influence of different management practices on SOC.
Ms Bolt says: “In the report we look at how different approaches, such as oversowing versus reseeding, or bagged fertiliser versus farmyard manure, affected levels of SOC.
“We used the information on management practices which farmers shared with us, alongside the soil samples.
“When making these comparisons, we also factored in the soil type for each field, as different soils have different capacities to store carbon.
Ms Bolt explains that knowing the texture of soil is key to understanding its restrictions and advantages, and how to manage it appropriately.
“Soils are very diverse, with the proportion of sand, silt and clay influencing its ‘workability’,” she says.
“Understanding the type of soil present in a field can help with knowing its restrictions, such as whether it is easily poached, and how to manage accordingly.
“Soil type also influences the capacity for a soil to store carbon.
“Clay particles are very small with a large surface area and are able to hold soil organic matter, preventing decomposition and release of CO2 into the atmosphere.
“This means soils composed of a higher proportion of clay have a greater capacity to store carbon.”
Ms Bolt explains that because soil type makes such a difference to the quantity of carbon stored, it is the organic carbon to clay ratio which is most useful to look at as a soil health indicator, as it shows whether a soil already has optimum level of carbon for its texture.
“It is also useful to calculate the total tonnes of carbon stored per hectare of soil, to understand what is currently being stored, and maximum attainable storage, taking into account the soil type,” she says.
“Full guidance on how to do this can be found in the report.
“This can be used to benchmark how much carbon is being stored in a farm’s soil over time, and we recommend analysing a soil sample every three to five years, to show the impact of management practices on SOC.”
Grassland soils can be managed to reduce carbon losses and to increase carbon inputs.
Ms Bolt says: “We saw a clear link between carbon inputs and SOC, with fields which had applications of manure to supply nitrogen containing more carbon than those which had received bagged inputs.
“In terms of reducing losses of carbon from soils, fields which had been reseeded using oversowing or direct drilling had higher levels of SOC than those which had been cultivated or ploughed.
“Another key finding was that SOC carbon tended to be highest under permanent pasture. In grass leys, the longer the ley duration, the higher the level of SOC.”
SOC could provide a basis for environmental payments in England under Environmental Land Management scheme, because it is a reliable indicator of soil health.
“Farmers will need to understand the current levels of organic carbon in their soil, as well as the level of SOC which is possible given the soil texture,” she says.
“Appropriate goals will need to be set based on this information, which should inform the payment received.”
David Cotton farms 223 hectares (550 acres) in Somerset, with 250 cows, 350 youngstock and 32ha (80 acres) in winter wheat.
He contributed a sample from one of his fields for the SOC report.
He says: “Being able to show how much carbon is stored in soils on UK dairy farms, rather than going into the atmosphere, is going to be a key tool for the sector to bust the myths around livestock farming,” says Mr Cotton.
On-farm, he intends to use the SOC results and report to help inform land management decisions, like how often to reseed.
“My aim is to achieve as much yield from forage as possible,” he says.
“We are already reducing soil movement by direct drilling our short-term leys and using minimum tillage when planting winter wheat.
“With less disturbance to the soil, we should minimise both carbon losses and nutrient run-off.
“It will be useful to repeat the soil analysis in three to five years, to see the impact of our approach on the amount of carbon stored.
“I see carbon storage analysis becoming something I do alongside N, P, K and pH testing, as I feel it is really important to pay attention to all aspects of the soil.”