In this article, we explained soil carbon sequestration, how soil carbon sequestration works, measuring soil carbon sequestration, the benefits, the global potential of soil carbon sequestration and the future.
Definition
Soil carbon sequestration is the process of capturing atmospheric carbon dioxide and storing it in the soil as organic matter. This natural process helps reduce greenhouse gases in the atmosphere, mitigating climate change. In addition to environmental benefits, soil carbon sequestration improves soil health, leading to better water retention, nutrient availability, and crop yields.
How Soil Carbon Sequestration Works:
Photosynthesis: Plants absorb from the atmosphere and, using sunlight, convert it into organic compounds.
Biomass Transfer: This carbon is stored in plant biomass (leaves, stems, and roots) and transferred to the soil when plant matter, such as fallen leaves and dead roots, decomposes.
Decomposition and Humus Formation: Soil microbes break down this organic material. Through this process, some of the carbon is converted into a stable, long-lasting form of organic matter called humus.
Long-term Storage: This stable organic carbon, or soil organic carbon (SOC), can be stored in the soil for long periods, effectively removing from the atmosphere. Practices that enhance soil carbon sequestration No-till or reduced tillage: Minimizing soil disturbance prevents the release of stored carbon.
Cover cropping: Planting cover crops between main harvests protects the soil and adds biomass. Crop rotation: Rotating different crops improves soil health and biodiversity, which supports more carbon sequestration.
Adding organic matter: Applying compost or using biochar adds carbon-rich material that soil microbes can process into stable humus.
Planned grazing: Rotational grazing can promote soil health and carbon storage through the decomposition of manure and urine.
Measuring Soil Carbon Sequestration:
Measurement-based approach Baseline sampling: Collect soil samples using a systematic approach to get a representative average from an entire field.
Lab analysis: Send samples to a lab for analysis of their SOC content using methods such as dry combustion or wet digestion.
Dry combustion: Involves heating the soil to a very high temperature to decompose carbon and measure the resulting carbon dioxide.
Wet digestion: Uses chemicals like potassium dichromate and sulfuric acid to oxidize the carbon in the soil sample.
Repeat measurements: Conduct the same sampling and lab analysis process at the same locations at intervals of several years to track changes in SOC over time.
Calculate stock: Use the lab results, along with the soil’s bulk density and thickness, to calculate the total soil organic carbon stock using the formula: Thickness Model-based approach Use of models: Employ computer models that use soil type, climate, and management practices to estimate carbon sequestration.
Hybrid approach: Combine modeling with periodic, targeted soil measurements.
Models can provide year-to-year estimates.
Measurements are used to validate the model’s performance and ensure accuracy over time.
Continuous improvement: Some advanced models can be continuously updated with data from new soil samples to improve their accuracy over time. Key considerations Representative sampling: Due to variations in soil across a field, taking a large number of samples from the same locations over time is crucial for accuracy.
Cost and labor: Measurement-based methods can be expensive and labor-intensive due to the extensive sampling and lab work required.
Model-only protocols: Some markets favor model-only approaches to reduce costs, but this may require careful validation to ensure credit accuracy.
The Benefits of Soil Carbon Sequestration:
Environmental benefits Climate change mitigation: Sequestering carbon in soils helps lower atmospheric concentrations, which is essential for slowing global warming.
Improved soil health: Increased soil organic matter improves soil structure, enhances water retention, and increases resistance to drought.
Biodiversity and ecosystem services: Healthy soils with high carbon content support a more diverse range of soil-dwelling organisms and strengthen ecosystem services. Agricultural benefits Increased crop yields: Higher soil fertility leads to better plant growth and can result in higher crop yields.
Reduced fertilizer use: Enhanced soil fertility can lead to a reduced need for chemical nitrogen fertilizers, which are energy-intensive to produce.
Greater resilience: Improved soil health makes farmland more resilient to extreme weather events caused by climate change. Economic benefits Income from carbon credits: Farmers can generate income by selling carbon credits for sequestering carbon in their soil.
Rural economic growth: Adoption of sustainable farming practices creates jobs and stimulates local economies.
Lower input costs: Reduced need for chemical fertilizers can lead to lower input costs for farmers.
The Global Potential of Soil Carbon Sequestration:
Annual sequestration potential: Estimates suggest soil carbon sequestration could potentially sequester from 0.6 to 1.2 Pg C/year, with some projections reaching 2–5 GtCO2/year by 2050.
Cumulative potential: The cumulative potential over the century is estimated to be between 104 and 130 GtCO2.
Contribution to emissions reduction: Soil carbon sequestration on agricultural lands could offset about 4% of annual global human-induced GHG emissions and is considered a cost-effective strategy for climate change mitigation.
Methods and their potential
Restoration of degraded soils: Restoring degraded and decertified soils has a technical potential of 0.6 to 1 billion metric tons of carbon per year.
Organic fertilizers: Applying organic fertilizers has the highest potential, estimated at 592 million metric tons of carbon per year globally.
Cover crops: The use of cover crops shows significant potential, particularly in certain climate zones, with a global potential of 153 million metric tons of carbon per year.
Reduced tillage: Reduced tillage methods are also effective, with a potential of 227 million metric tons of carbon per year globally.
Inorganic fertilizers: Inorganic fertilization has the lowest potential among the methods assessed, estimated at 78 million metric tons of carbon per year globally.
Climate zone: The potential varies significantly by climate zone. For instance, subtropical regions show higher potential for organic fertilizers and cover crops compared to temperate zones.
Soil conditions: Focusing on agricultural soils with large yield gaps and/or low soil organic carbon (SOC) levels offers the greatest potential for improvement.
Management practices: The full potential can only be achieved through supportive policies, knowledge transfer, and incentives that encourage widespread adoption of effective practices.
The Future of Soil Carbon Sequestration:
Research and development
Understanding limitations: Future research will focus on addressing limitations like saturation, reversibility, and the impact of varying soil types, nutrients, and weather patterns.
Improving measurement: Scientists are working on more accurate and cost-effective ways to measure and verify the amount of carbon being sequestered, which is crucial for carbon credit systems.
Advanced techniques: Research is exploring advanced techniques such as enhancing root phenotypes to allocate carbon deeper in the soil, using perennial crops, and developing new management practices.
Encouraging adoption: Policies and incentives are needed to encourage the widespread adoption of soil carbon sequestration practices by farmers.
Incentive programs: Programs are being developed to link soil carbon sequestration with climate change mitigation efforts, including those outlined in the UN’s climate conventions.
Carbon credits: The growth of carbon markets that offer credits for sequestered soil carbon is expected to increase the financial viability of these practices for landowners.
Widespread adoption: The future involves a move from theoretical potential to practical, large-scale implementation through practices like conservation agriculture, no-till farming, cover cropping, and the use of composted manure.
Economic viability: A key challenge is ensuring that the practices are economically feasible for farmers, with potential for higher yields and reduced input costs as co-benefits.
Integrated approach: The future will likely see a more integrated approach that combines carbon sequestration with other soil health benefits, such as improved water retention and nutrient cycling, which enhances long-term agricultural productivity.
Conclusion
Soil carbon sequestration is the process of capturing atmospheric carbon dioxide (\(\text{CO}_{2}\)) and storing it in the soil as organic matter. This natural process, enhanced by specific land management practices, helps mitigate climate change while also improving soil health and agricultural productivity.