By David Okul
SOC is a measurable part of soil organic matter (SOM). SOM is notoriously difficult to measure and makes up 2-10% of soil. It contributes to carbon sequestration, soil structure, moisture retention, and biological functions of soils.
SOM is divided into living and dead components and varies from recent to century-old inputs. Its matter includes dissolved organic matter, particulate organic matter, humus, and resistance organic matter.
Estimating SOM from SOC
A conversion factor of 1.724 (to SOC) provides a reasonable estimate of soil organic matter for most purposes. The assumption is based on the observation that organic matter is 58% carbon.
However, Douglas Prybil (2010) refutes the claim. He claims that the factor is too low for most soils as the median conversion factor is 1.9 from their study. Their study concluded that a factor of 2 would be more practical as the values range from 1.4 to 2.5.
In summary, the factor of 1.724 is based on early studies and needs urgent inspection or revision.
SOC Sequestration
SOC sequestration refers to the process where carbon dioxide is transferred from the atmosphere into the soil as organic carbon. The process starts with photosynthesis where atmospheric carbon dioxide is transferred to organic compounds. The compounds are subsequently incorporated into the soil via plant residues and root exudates. Apart from that, other sources of SOC include:
- Byproducts of animal and microbial activity
- Organic compounds incorporated through dead plants and leaves with the assistance of subterranean organisms.
SOC sequestration is fronted as one of the ways in which climate change could be mitigated. It is argued that small increases of SOC in very large areas of agricultural and pastoral lands would significantly reduce atmospheric Carbon dioxide.
Various strategies could help optimize SOC sequestration potential including:
- Conservation tillage: it involves minimal soil disturbance
- Crop rotation: it helps to vary plant residues
- Cover cropping: These are often plowed under the ground to add more carbon
- Organic amendments: For instance compost and manure that increase organic matter in the soil
The potential of SOC sequestration is influenced by other factors such as
- Rainfall
- Soil erosion
- Temperature
- Sediment deposition
For the reduction to be permanent, the organic matter would be in a stable or resistant faction. Scientists estimate that grasslands have the potential to sequester 6.5 billion metric tonnes per year and close to 1.85 billion metric tonnes of carbon per year for croplands.
Measuring SOC is not a simple task as sampling needs to be systematic to represent the entire field. As SOC is dynamic, measurements are often associated with some degree of uncertainty.
The restoration of grassland ecosystems is explored as a means of accelerating SOC sequestration as soils store climatically significant amounts of SOC. Future research needs to focus on factors that influence sequestration rates, the development of accurate monitoring techniques, and the establishment of policies conducive to sequestration.
Concluding Remarks
The science of SOC sequestration is rapidly evolving and is incorporating the use of AI and satellite imagery. Given the expanse of grassland and agricultural land, we think that SOC sequestration offers a feasible solution for SOC sequestration. Monitoring SOC could greatly enhance carbon markets as both avoidance and reduction carbon projects could be developed from soil-related conservation activities.
Additional reading
David Okul is an environmental management professional with over 10 years of experience in donor projects, conservation, forestry, ecotourism, and community-based natural resources management. When not working on environmental projects, I spend my time writing for Silvica on a variety of topics.
