Soil Organic Carbon Sequestration: Taking A Closer Look

What Is Soil Organic Carbon Sequestration

Soil carbon sequestration (SOC) is the process of transferring CO2 from the atmosphere into the soil in the form of organic carbon. This process begins with photosynthesis, where plants convert atmospheric carbon dioxide into organic compounds. These compounds are then incorporated into the soil through plant residues and root exudates.

SOC is the carbon fraction of soil organic matter, derived not only from plants but also from animals and microorganisms. Another source of these compounds is the byproducts of animal and microbial activity.

The process of carbon sequestration in soil continues as organic compounds are incorporated into the earth through dead plants or leaves. These materials eventually decompose and transform into SOC with the help of subterranean organisms.

Since by increasing the soil’s organic carbon content we can effectively lock away CO2 – a major greenhouse gas that traps heat in the atmosphere – from the air, SOC sequestration also turns out to be a natural way of mitigating climate change.

Soil Carbon Sequestration Potential

Utilizing soil carbon sequestration for climate change mitigation holds immense potential. Today, farmers and agribusinesses can employ a variety of strategies to enhance this process:

• Conservation tillage. Traditional tilling exposes organic matter in the soil to oxygen, which aids decomposition, releasing CO2 and other greenhouse gases. Conservation tillage, on the other hand, involves minimal soil disturbance, which helps to retain soil carbon.
• Crop rotation and diversification. This practice can enhance SOC levels by varying the amount and type of plant residues returned to the soil. Different crops have different root structures and growth patterns, which can influence soil carbon sequestration.
• Cover cropping. Clover, beans, peas, and other cover crops planted after the main crop is harvested help carbon get into the ground year-round. These crops can be plowed under the ground as “green manure,” adding more carbon to the soil.
• Applying Organic Amendments. Compost and manure can significantly increase SOC levels and enhance erosion control measures like contour plowing and terracing. These amendments increase organic matter in the soil, which improves its structure and enhances its ability to absorb and retain water. For example, perennial crops, which do not die off every year, grow deep roots that help soils store more carbon.

However, the potential for carbon sequestration in soil is influenced by local controls on ecosystem processes such as rainfall infiltration, soil erosion and temperature, and sediment deposition. These factors can vary on local scales due to landscape heterogeneity, affecting SOC input and loss rates, and resulting in differences in SOC contents along topographic gradients ^{James A, Thompson, Randall K. Kolka (2005). Soil carbon storage estimation in a forested watershed using quantitative soil-landscape modeling. Soil Science Society of America Journal 69:1086-1093. https://doi.org/10.2136/sssaj2004.0322.}. For example, slope position impacts soil moisture and nutrient levels, with subsequent impact on plant root growth that may have consequences for SOC ^{Joan G. Ehrenfeld, Eric Kaldor, Robert W. Parmelee (December, 1992). Vertical distribution of roots along a soil toposequence in the New Jersey Pinelands. Canadian Journal of Forest Research. 22(12): 1929-1936. https://doi.org/10.1139/x92-252.}.

The potential for carbon sequestration in soil may be determined by understanding both the historic SOC stocks under natural vegetation prior to conversion to the uses and the influences of those land uses on carbon loss. Changes in land use and management that result in either increased inputs or decreased losses of SOC can reduce its deficit and enhance soil carbon sequestration.

Scientists estimate that soils, primarily agricultural ones, could sequester over a billion additional tons of SOC each yet ^{Soil-Based Carbon Sequestration. (April 15, 2021). The MIT Climate Portal.}. Grasslands present a significant opportunity for soil organic carbon sequestration, with the potential to absorb carbon equivalent to about 6.5 billion metric tons per year ^{Sha, Z., Bai, Y., Li, R. et al (Jan 18, 2021). The global carbon sink potential of terrestrial vegetation can be increased substantially by optimal land management. Communications, Earth & Environment 3, 8 (2022). https://doi.org/10.1038/s43247-021-00333-1.}. It is roughly equivalent to carbon offsetting the annual emissions of over 1,400 coal-fired power plants. As for croplands, they could sequester between 0.90 and 1.85 billion metric tons of carbon per year, accounting for 26-53% of the target set by the ‘4p1000 Initiative: Soils for Food Security and Climate’, a global strategy to leverage soil for climate change mitigation ^{Zomer, R.J., Bossio, D.A., Sommer, R. et al (Sept 15, 2021). Global Sequestration Potential of Increased Organic Carbon in Cropland Soils. Scientific Reports 7, 15554 (2017). https://doi.org/10.1038/s41598-017-15794-8.}.

How To Measure Carbon Sequestration In Soil

Measuring soil carbon sequestration is a crucial step for farmers and agribusinesses wanting to reap financial benefits from their efforts. To do this, they need to employ careful sampling strategies and bring collected soil to a lab to determine its SOC content.

This is not a simple task, as sampling requires a systematic approach to ensure that the samples are representative of the entire field.

Once the samples reach the lab, they undergo a complex process to measure and verify the SOC content. This involves a variety of techniques and methodologies, as carbon levels can significantly vary both over time and across different field areas. For instance, the SOC content can differ between the topsoil and subsoil layers, and even within the same layer, it can vary depending on the soil type, climate, and management practices.

Based on the lab results, estimates of soil carbon sequestration are made in comparison to the baseline state. However, given the complexity of SOC dynamics, these estimates are often associated with a degree of uncertainty.

To overcome this challenge, scientists use various change estimation models. Some of them simulate the processes involved in carbon cycling in soil, such as the decomposition of organic matter, carbon input from plant residues, and its loss through respiration. Others are based on already observed relationships between SOC and influencing factors and use statistical techniques to predict SOC changes on historical data.

There are also hybrid models that combine elements of process-based and empirical models. These models leverage the strengths of both approaches, providing more accurate and reliable estimates of the effects of soil carbon sequestration.

Since businesses want to know possible profits before engaging in any new venture, they can forecast the amount of sequestered SOC using modern AI-powered satellite analytics solutions. For that, they need to take soil samples so that the analytics model could use them as a baseline.

After a certain period of time – the longer, the better for more noticeable changes – the user will need to take only 10% of the initial samples again to validate the model. This approach significantly reduces the time and cost associated with soil sampling, making it a more feasible option for businesses.

Current And Upcoming Researches And Inventions In SOC Sequestration

The field of soil carbon sequestration is rapidly evolving, with numerous research studies and technological advancements contributing to our understanding and ability to harness this powerful tool for climate mitigation changes.

One area of focus is the potential of grasslands for carbon sequestration in soil. A study published in Science highlighted that global grasslands could sequester between 2.3 to 7.3 billion tons of CO2 equivalents per year through biodiversity restoration, improved grazing management, and the introduction of sown legumes in pasture lands ^{Yongfei Bai, M. Francesca Cotrufo (2022). Grassland soil carbon sequestration: Current understanding, challenges, and solutions. Science, Vol 377, Issue 6606. https://doi.org/10.1126/science.abo2380.}.

The restoration of grassland ecosystems is also being explored as a means to accelerate SOC sequestration. Research indicates that soils store climatically significant amounts of carbon as organic matter, globally about 2.3 times greater than the carbon in atmospheric CO2 and 3.5 times greater than the carbon in all living organisms ^{Yang, Y., Tilman, D., Furey, G. et al. Soil carbon sequestration accelerated by restoration of grassland biodiversity. Nat Commun 10, 718 (2019). https://doi.org/10.1038/s41467-019-08636-w.}.

Another significant area of research is the role of fertilizers in sustainable soil carbon sequestration. A study in Nature revealed that such sequestration often requires large amounts of mineral fertilizers, particularly to replace nutrients ^{Amelung, W., Bossio, D., de Vries, W. et al. Towards a global-scale soil climate mitigation strategy. Nat Commun 11, 5427 (2020). https://doi.org/10.1038/s41467-020-18887-7.}.

Looking ahead, the future of SOC sequestration research is likely to involve further exploration of the factors that influence sequestration rates, the development of more accurate measurement and verification techniques, and the creation of policies and incentives to encourage the adoption of soil carbon sequestration practices.

SOC Management And Modern Technologies

Modern technology, particularly AI-powered satellite data analytics, is playing a pivotal role in overcoming the challenges of measuring soil carbon sequestration.

Satellite images provide high-resolution data on SOC levels across large geographical areas. AI models analyze historical and current data to predict changes in SOC levels based on various factors such as land use, climate, and management practices. And then the insights provided by AI-powered satellite analytics can guide farmers toward more sustainable and carbon-efficient practices.

On a larger scale, reliable data on soil health and carbon sequestration can inform policy decisions promoting sequestration practices that mitigate climate change. The advances in technologies have also led to the introduction of a carbon market as a way to stimulate SOC sequestration.

SOC Sequestration As A Pathway To A Greener Tomorrow

The more we learn about organic carbon and its role in sequestration, the more we realize its potential in addressing our most pressing environmental challenges. Although the science of carbon sequestration in soil is rapidly evolving, the potential of the Earth to sequester carbon is immense, and we have only just begun to tap into it.

The journey towards a more sustainable and carbon-conscious future is a challenging one, but it is a journey we must undertake. By deepening our understanding of soil organic carbon sequestration, we will provide the knowledge and tools needed to harness the power of the earth for the benefit of our planet and future generations.