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Soil Organic Carbon

  • Soil Health

  • Chemical


Soil organic carbon plays a pivotal role in influencing crucial functional processes within the soil, encompassing nutrient storage, particularly for nitrogen, water retention capacity, and the stability of soil aggregates. Furthermore, it exerts a substantial impact on microbial activity, thus establishing itself as an integral constituent of soil fertility (Cardoso et al., 2013).

Soil organic carbon has been directly associated with several significant ecosystem services, including carbon sequestration, climate regulation, biomass production, the filtrating, buffering, and transformation of substances, as well as the preservation of genetic diversity within ecosystems (Guerra et al., 2021).

The percentage of organic matter is determined by loss on ignition, based on the change in mass after a soil is exposed to high temperature (500 °C or 932°F) in a furnace.

Methodology summary

To determine soil organic carbon by loss of ignition:

  • A sample is dried at 105°C to remove all water.
  • The sample is weighed.
  • The sample is then ashed (for weight loss on ignition) for two hours at 500°C, and the percent of mass lost is calculated after weighing again.
  • The % loss on ignition (LOI) is converted to % organic matter (OM) using the following equation: % OM = (% LOI * 0.7) – 0.23 (CASH 2016)
  • In the LOI method some laboratories can use different ignition temperature, so it is recommended to use the same laboratory and keep record of the temperature used by the laboratory.

Detailed information on how to monitor soil organic carbon

The guide includes:

  • How to sample within fields?
  • At what depths should samples be taken?
  • How often should you repeat your sampling?
  • How to collect and prepare your samples?
  • What are the options for the lab analyses?

Metric threshold or direction of change

In general higher soil organic carbon is considered good for soil health as it can provide nutrition for microbes and release nutrients for plant growth, as well as improve soil structure and water-holding capacities. Thresholds will depend on the type of habitat, vegetation cover and soil type. In general, in the UK it is difficult to define a specific threshold as it can range from 5 % in light coarse-textured soils in arable land to 95 % in wetlands with carbon-rich soils, as benchmarked by the UKCEH (Feeney et al., 2023).

Technological innovations

Near-Infrared Spectroscopy (NIRS) can be employed for soil organic carbon measurement by examining the relationship between soil spectral reflectance and the spectral characteristics of soil organic matter. This approach has demonstrated efficiency and cost-effectiveness. Calibration of NIRS models necessitates the utilization of a well-representative dataset of soil samples, accompanied by corresponding laboratory measurements. The calibration process, while effective, can be time-consuming and demands expertise to ensure precise predictions. NIR models developed for a specific region may not be universally applicable to other regions due to variations in soil properties, climate, and vegetation (Long et al., 2023).


  • Agricultural
  • Forest
  • Grassland
  • Peatland
  • Saltmarsh
  • Wetland


  • Community


  • Medium


  • Tier 1

Technical expertise

  • Low

Standardised methodology

  • Yes