1. Introduction Soil organic carbon (SOC) is the carbon present in the organic fraction of soil. It originates mainly from crop residues, roots, microorganisms, animal residues and organic amendments. SOC is an important component of soil organic matter and contributes to nutrient cycling, water regulation, soil structure and other soil functions. FAO identifies SOC management as an important component of sustainable soil management and climate action. Maintaining and increasing SOC can improve soil quality and support sustainable agricultural production. However, SOC levels differ among soils because they are influenced by climate, vegetation, soil properties, land use and management practices. 2. What is Soil Organic Carbon? Soil organic carbon is the carbon contained in soil organic matter. Organic matter includes materials such as plant residues, roots, animal residues, compost and microbial biomass at different stages of decomposition. SOC is the carbon component of this organic material. A simple pathway is: Soil Organic Carbon Pathway Crop Residues& Roots → Decomposition → Soil OrganicMatter → Soil OrganicCarbon → SoilFunctions Figure: Simplified pathway showing how plant-derived organic inputs contribute to soil organic carbon and soil functions. SOC concentration is commonly expressed as a percentage or mass of carbon per unit mass of soil. SOC stock, in contrast, represents the quantity of carbon stored in a defined soil depth and area. 3. Why Soil Organic Carbon Matters SOC supports several important soil functions. Soil structure: Organic carbon contributes to the formation and stability of soil aggregates. Nutrient cycling: Organic materials provide carbon and nutrients that are transformed by soil organisms. Water management: Soil organic matter contributes to water retention and infiltration. Soil biological activity: Organic carbon provides energy and substrates for microorganisms and other soil organisms. Erosion protection: Improved aggregation and soil cover can reduce soil susceptibility to erosion. Climate regulation: Soil is a major terrestrial carbon reservoir. Changes in soil carbon can influence exchanges of carbon dioxide between soils and the atmosphere. ICAR's soil-health programmes also emphasize balanced nutrient management, organic inputs and maintenance of soil carbon as components of sustainable soil management. 4. Major Sources of Soil Organic Carbon Carbon enters agricultural soils through several pathways: Crop residues such as straw, stalks, leaves and roots Root exudates and dead roots Farmyard manure Compost and vermicompost Green-manure crops Cover crops Intercrops and diversified cropping systems Biomass from agroforestry Biochar and other suitable carbon-rich amendments The quantity of carbon added to soil does not directly determine the quantity ultimately stored. Decomposition, microbial activity, soil texture, mineral interactions, climate and management influence carbon retention. FAO's Recarbonizing Global Soils manual identifies 49 sustainable soil-management practices relevant to maintaining or increasing SOC across different agricultural and integrated farming systems. 5. Factors Affecting Soil Organic Carbon SOC varies between fields and regions because several factors control carbon inputs and losses. Climate: Temperature and soil moisture influence decomposition and carbon turnover. Soil texture: Clay and fine mineral particles can contribute to the protection and stabilization of organic carbon. Cropping system: Crop type, biomass production, rooting pattern and residue quantity affect carbon inputs. Tillage: Soil disturbance can alter aggregation and carbon turnover. The effect of tillage on SOC depends on soil, climate, residue management and the depth considered. Organic inputs: Manure, compost, crop residues and green manures increase carbon inputs when appropriately managed. Erosion: Removal of carbon-rich topsoil can reduce SOC stocks. Land-use history: Previous vegetation, cultivation and management practices influence present SOC levels. Consequently, SOC management should be adapted to local soil, climate, crop and farming conditions rather than relying on a single practice for all locations. 6. How Soil Organic Carbon Is Measured Reliable SOC assessment requires representative soil sampling and appropriate laboratory analysis. Soil sampling Soil samples should be collected using a defined sampling depth, sampling pattern and number of sampling points. Sampling procedures should be consistent when SOC is being monitored over time. For estimating SOC stocks, soil bulk density is also required because carbon concentration alone does not indicate the total amount of carbon stored per unit area. Laboratory analysis Common approaches include: Dry combustion: Soil carbon is converted to carbon dioxide through controlled combustion and quantified using an appropriate carbon or elemental analyser. Dry-combustion methods are widely used for quantitative carbon analysis. Wet oxidation methods: Methods such as Walkley–Black have historically been widely used for estimating soil organic carbon. Their recovery can vary among soils and therefore the analytical method and its limitations should be considered. Spectroscopic methods: Near-infrared and mid-infrared spectroscopy can support rapid SOC estimation when appropriate calibration datasets and laboratory reference measurements are available. Estimating SOC stock SOC concentration should not be confused with SOC stock. A simplified representation is: SOC concentration should not be confused with SOC stock. SOCConcentration × BulkDensity × SoilDepth → SOCStock Figure: Conceptual representation of SOC stock estimation. The FAO GSOC-MRV protocol calculates SOC stock using organic-carbon concentration, fine-earth bulk density, coarse-fragment correction and soil-layer thickness. Therefore, two soils with the same SOC concentration can have different carbon stocks if their bulk densities or soil depths differ. For monitoring purposes: Soil Organic Carbon Monitoring Workflow SoilSampling → LaboratoryAnalysis → SOCConcentration → BulkDensity → SOCStock → RepeatedMeasurement Figure: Soil organic carbon monitoring workflow. FAO recommends standardized approaches for measuring, monitoring and reporting SOC so that changes in soil carbon can be assessed reliably over time. 7. Practices to Increase and Maintain Soil Organic Carbon Farmers can improve or maintain SOC by increasing organic-carbon inputs, reducing avoidable losses and protecting soil from degradation. ICAR identifies manure, balanced fertilizer use, reduced or zero tillage, crop-residue management, integrated nutrient management, biochar, cover crops, intercropping and pulse-based rotations among practices that can contribute to soil-carbon sequestration. Important practices include: Crop-residue management: Retaining suitable crop residues can return carbon to the soil and protect the soil surface. Cover crops: Cover crops increase biomass inputs and maintain soil cover between principal crops. Crop rotation and diversification: Rotations involving legumes and diversified crops can increase the diversity and continuity of carbon inputs. Reduced or conservation tillage: Reduced soil disturbance can influence SOC dynamics, particularly when combined with residue retention and appropriate nutrient management. Field research in India's Indo-Gangetic Plains has reported greater SOC pools under conservation-agriculture treatments with residue retention than under conventional tillage with residue removal. Organic amendments: Farmyard manure, compost and other suitable organic materials can contribute carbon and nutrients to soil. Agroforestry: Integration of trees with agricultural systems can add carbon through above-ground biomass, roots and litter. Biochar: Appropriately produced biochar can provide a relatively stable carbon pool when its production, quality, application and accounting are properly managed. No single practice is suitable for every farm. Selection should consider soil type, climate, crop, water availability, residue availability, labour and local economic conditions. 8. Soil Organic Carbon and Climate Change Soils contain a large terrestrial carbon pool. FAO reports that the top 30 cm of soil globally contains more carbon than the atmosphere and vegetation combined. Unsustainable soil management can release stored carbon, whereas appropriate sustainable soil-management practices can increase or maintain SOC stocks. A simplified pathway is: Conceptual Pathway Linking Sustainable Soil Management with Soil-Carbon Sequestration and Climate Mitigation Sustainable SoilManagement → Increased Carbon Inputs/ Reduced Losses → Higher SOCStocks → Potential AtmosphericCO₂ Removal → ClimateMitigation Figure: Conceptual pathway linking sustainable soil management with soil-carbon sequestration and climate mitigation. FAO's RECSOIL initiative focuses specifically on increasing and maintaining SOC through sustainable soil management while improving soil health, agricultural resilience and farmer livelihoods. However, increased SOC should not automatically be treated as permanent carbon removal. Soil carbon can subsequently decline if management changes or environmental conditions cause carbon losses. Therefore, climate claims require appropriate measurement, monitoring and accounting. 9. Soil Carbon and Carbon Credits Soil-carbon management can potentially contribute to carbon-credit projects when an approved carbon-crediting methodology permits the resulting emission reductions or removals to be quantified. For example, Verra's VM0042 Improved Agricultural Land Management, v2.2 quantifies GHG emission reductions and SOC removals resulting from improved agricultural land management. The methodology includes practices such as reduced tillage, fertilizer management, biomass-residue management, water management, cover crops, crop management and grazing practices. It has been active since 21 October 2025. A critical distinction is: SOC increase is not equal to automatically one carbon credit A carbon-credit project requires an applicable methodology and appropriate accounting of baseline conditions, project activities, additionality where applicable, monitoring, uncertainty and verification. Verra's VM0042 specifically contains requirements for quantifying SOC changes and associated GHG emission reductions/removals. 10. Practical Recommendations for Farmers Farmers can consider the following actions: Test soil through an appropriate soil-testing laboratory. Follow soil-health and nutrient-management recommendations. Retain suitable crop residues instead of routinely burning them. Use crop rotations and diversified cropping systems. Include legumes or cover crops where agronomically appropriate. Apply well-managed organic amendments according to crop and soil requirements. Minimize unnecessary soil disturbance. Maintain soil cover to reduce erosion. Improve water and nutrient-use efficiency. Maintain farm records if participating in a carbon project. SOC changes should be assessed over multiple sampling periods rather than inferred from a single soil measurement. FAO emphasizes standardized measurement, monitoring, reporting and verification for reliable assessment of soil-carbon changes. 11. Core Insights SOC is an important indicator of soil health. Crop residues, roots, manure, compost, cover crops and diversified cropping systems can provide carbon inputs. Conservation agriculture and residue management can improve SOC under suitable conditions. SOC concentration and SOC stock are different measurements. SOC-stock estimation requires appropriate soil sampling, carbon concentration, bulk density and soil-depth information. Sustainable soil management can contribute to climate-change mitigation and agricultural resilience. An increase in SOC does not automatically constitute a carbon credit. Carbon-credit projects require an applicable methodology, monitoring and verification. Farmers should examine project methodology, contractual terms, monitoring costs and benefit-sharing arrangements before joining a carbon project. 12. References Food and Agriculture Organization of the United Nations. (2020). GSOC-MRV protocol: A protocol for measurement, monitoring, reporting and verification of soil organic carbon in agricultural landscapes. Global Soil Partnership.Full link: https://www.fao.org/fileadmin/user_upload/GSP/MRV/GSP_MRV_Protocol_A4_EN_002.pdf Singh, V. K., Kundu, S., & Naveen, J. (2023). Soil carbon management for sustainable food system. Indian Farming, 73(6), 2529.Full link: https://epubs.icar.org.in/index.php/IndFarm/article/view/138317/ Kundu, S., Srinivasarao, C., Reddy, K. S., Prasad, J. V. N. S., Indoria, A. K., Veni, V. G., & Singh, V. K. (2022). Soil carbon management in rainfed production systems. Indian Farming, 72(11).Full link: https://epubs.icar.org.in/index.php/IndFarm/article/view/131390 Indian Council of Agricultural Research. (2023, May 22). National Campaign on Soil Health Management (Nutrient Use Efficiency and SOC Management).Full link: https://www.icar.gov.in/en/national-campaign-soil-health-management-nutrient-use-efficiency-and-soc-management Ministry of Agriculture & Farmers Welfare, Government of India. (2024, January 29). Launch of Framework for Voluntary Carbon Market in Agriculture Sector and Accreditation Protocol of Agroforestry Nurseries. Press Information Bureau.Full link: https://www.pib.gov.in/Pressreleaseshare.aspx?PRID=2000331&lang=2®=48 Ministry of Agriculture & Farmers Welfare, Government of India. (2024, July 26). Carbon Trading Mechanism in Agriculture Sector. Press Information Bureau.Full link: https://www.pib.gov.in/Pressreleaseshare.aspx?PRID=2037660&lang=2®=48 Food and Agriculture Organization of the United Nations. (n.d.). Asia-Pacific knowledge hub on sustainable soil and land management: GSOC-MRV Protocol.Full link: https://www.fao.org/asiapacific/work-in-the-region/regional-priorities/faorap-regional-priority-two/soil-management/capacity-building-and-knowledge-exchange/asia-pacific-knowledge-hub-on-sustainable-soil-and-land-management/en Verra. (2025). VM0042 Improved Agricultural Land Management, v2.2.Full link: https://verra.org/methodologies/vm0042-improved-agricultural-land-management-v2-2/ Dinesh, G. K. (2026, September 11). Carbon credits from agriculture: Opportunities for farmers and sustainable soil management. Vikaspedia.Full link: https://agriculture.vikaspedia.in/viewcontent/agriculture/policies-and-schemes/soil-related/carbon-credits-from-agriculture-opportunities-for-farmers-and-sustainable-soil-management?lgn=en Dinesh, G. K., Sinduja, M., Priyanka, B., Sathya, V., Karthika, S., Meena, R. S., et al. (2022). Enhancing soil organic carbon sequestration in agriculture: Plans and policies. In Plans and Policies for Soil Organic Carbon Management in Agriculture, pp. 95–121. https://doi.org/10.1007/978-981-19-6179-3_4 Dinesh, G. K., Venkatramanan, V., Jayaraman, S., Bolan, N., Srinivasa Rao, C., Meena, R. S., et al. (2025). Carbon farming: Ecosystem services and its potential in achieving UN Sustainable Development Goals. Advances in Agronomy, 196, 201–378. https://doi.org/10.1016/bs.agron.2025.10.002 Cite this page as Dinesh, G. K. (2026). Soil Organic Carbon: Importance, Measurement and Management for Sustainable Agriculture. Vikaspedia under MEITY, CDAC, Government of India. https://data.vikaspedia.in/short/lc?k=iCH8TqkHeyC1O8F88fI4tQ