Recent interest in carbon trading and the Government’s Net Zero by 2050 target has led to an increase in enquiries at NRM laboratories relating to Soil Carbon, Organic Matter and the link between them. Agriculture can play a significant role in carbon sequestration, with soil providing a huge carbon sink. Understanding the soil and what percentage is made up of carbon plays a key part in being able to effectively manage and increase the carbon stock percentage. The launch of the Environment Land Management Scheme (ELMS) is likely to create more reasons for landowners and farmers to understand their carbon stock. Although the details are not confirmed, it is expected that Soil Health and Carbon stocks will form part of the scheme.
In response to the increased interest, NRM laboratories have developed a comprehensive package which provides an accurate assessment of the carbon stored in soils, applicable to both grassland and arable systems. CarbonCheck provides not just an organic carbon stock figure but also a range of other useful parameters. It uses a combination of individually tested parameters and calculations to determine carbon figures and provides users with a report to enable action to be taken and comparisons to be made. It is recommended that sampling should be carried out regularly to monitor changes in soil carbon stock levels, ideally at the same time of year to reduce sampling variation.
The Bulk Density of a soil gives a good indication of how well plant roots can grow and explore the soil for nutrients, and how easily air and water can move within the soil profile. The Bulk Density of the soil is used to calculate the Organic Carbon Stock. This is carried out using the ‘disturbed scoop’ method. This is different to the undisturbed core method. The scoop method was chosen over alternative methods due to the positive supporting evidence regarding this method.
Sampling Depth and Stone Content details are provided by the sampler on the sample paperwork. This allows the laboratory to determine the soil coverage per square meter. Providing this background data ensures a more accurate assessment of the carbon stock in the soil.
Inorganic Carbon also known as Soil Inorganic Carbon (SIC) comprises of carbonates and bicarbonates which are abundant in chalky soils. The calcium carbonate content of the soil is determined from the SIC and means we can assess how calcareous the soil is.
Total Carbon % is determined using the combustion method, which is comparable with the Dumas method. Total carbon measures both inorganic and organic carbon forms in the soil.
Organic Carbon is then calculated by removing the Inorganic Carbon figure from the total Carbon figure. Also known as Soil Organic Carbon (SOC), it is the carbon component of soil organic matter. This diverse group of carbonbased compounds originates from the decomposition of plant material, animal residues, soil fauna and biota. The level of SOC is influenced by environmental factors and management practices. It is a key measurement in monitoring changes in the levels of carbon stocks. The report provides a visual representation of the SOC and SIC split.
Organic Matter % is a complex combination of all organic material found in the soil including living components (plant roots, microorganisms) and dead components (leaf litter, humic substances). Organic Matter increases the soil’s water holding capacity and provides a slow-release source of energy for micro-organisms, increasing the cycling of nutrients within the soil. This report uses the Van Bemmelen factor of 0.58 to convert Soil Organic Carbon to Organic Matter.
Total Nitrogen % is determined using the combustion method. Nitrogen is the main driver of plant growth and is associated with soil organic matter. It is mobile in the environment and present in many different compounds, some of which are available for uptake by plants. Total Nitrogen is the measure of all forms of nitrogen (organic and inorganic) in the dried sample.
C:N Ratio is calculated using the Total Nitrogen and Organic Carbon results. The proportion of organic carbon relative to nitrogen (C:N ratio) gives an indication of the right balance for soil microbes to support the release of nutrients. The optimal C:N ratio for nitrogen release in soil is between 10 and 12.
Organic Carbon Stock (t/ha) gives a total organic carbon value in tonnes of carbon per hectare of land to the specified sampling depth. This calculation factors in the measured soil organic carbon %, stone content, sampling depth and bulk density. There is also the option of upgrading the package to CarbonCheck Plus which provides an additional measure – Active Carbon. This parameter is also available as a stand-alone test.
Active Carbon (mg/kg) or Labile Carbon is the portion of carbon which readily breaks down and provides an active source of nutrition to soil microbes. The effect of changes in soil management such as cultivation methods or the use of cover crops can be monitored with active carbon analysis as it is a precursor to the long term build-up of organic matter. Understanding the Carbon Stock levels in the soil provides landowners with the opportunity to adjust land management practices to improve Organic Matter as well as providing future proofing against the imminent ELMS policy.
CarbonCheck is available direct from NRM Laboratories, or via your agronomist, advisor or soil sampling provider. You can get in touch with NRM for further information or to request your free sampling kit on 01344 886338.
