Soil Carbon Sequestration: How Farming Practices Translate into Verified Credits

There is a carbon bank underneath every farmer's field, and most farmers have no idea it is there.

Soil organic carbon, the carbon stored in decomposed plant matter, root systems, fungal networks, and microbial biomass in the soil, is one of the largest terrestrial carbon pools on Earth. Healthy agricultural soils can store enormous quantities of CO₂. Degraded soils have lost much of that storage capacity through tillage, erosion, chemical-intensive cultivation, and the removal of organic matter.

The good news for Indian farmers is that improving soil health and increasing soil organic carbon is achievable through farming practices that also improve agricultural productivity. And in an emerging set of carbon market methodologies, that improvement can now be converted into verified carbon credits.

What Is Soil Organic Carbon and Why Does It Matter?

Soil organic carbon (SOC) is the carbon component of organic matter in soil: the remains of plants, animals, and microorganisms in various stages of decomposition. It is sometimes referred to as humus, though that term technically refers to a specific fraction of highly decomposed organic matter.

SOC matters for at least three reasons that affect farmers directly.

First, it improves soil structure. Soils with higher organic carbon content have better aggregation: the particles clump together in a way that creates pore spaces, which improves water infiltration and retention. A soil that can absorb and hold more water is more resilient to both drought and flooding.

Second, it improves soil fertility. Organic carbon is the primary food source for soil microorganisms, bacteria, fungi, and invertebrates, that break down nutrients into plant-available forms. Soils with more organic carbon have more active microbial communities and release more nutrients to crops, often reducing the need for synthetic fertiliser inputs.

Third, it is the mechanism by which carbon dioxide from the atmosphere is transferred into the soil through plant photosynthesis and root decomposition. More organic carbon in the soil means less CO₂ in the atmosphere.

A farmer who adds organic matter back to the soil, reduces tillage, or integrates cover crops is doing three things simultaneously: improving their soil, reducing their input costs, and sequestering carbon.

Which Farming Practices Increase Soil Carbon?

Not every farming practice increases SOC. Some, deep tillage, mono-cropping without organic matter return, and long fallow periods, actively deplete it. But a range of practices that are already familiar to many Indian farmers can significantly improve soil organic carbon over time.

• Composting and organic matter return: applying farmyard manure, compost, or crop residue back to the soil rather than burning or discarding it. This is one of the most direct ways to add carbon to the soil, and it is also one of the oldest farming practices in India.

• Reduced or zero tillage: minimising soil disturbance during land preparation. Tillage exposes buried organic matter to oxygen, accelerating its decomposition and releasing stored carbon as CO₂. Reduced tillage slows this process and allows SOC to accumulate.

• Cover cropping: growing a secondary crop between main crop seasons specifically to cover and protect the soil, build organic matter, and fix nitrogen. Leguminous cover crops, in particular, add both carbon and nitrogen to the soil.

• Agroforestry: integrating trees into farming systems contributes significantly to SOC through leaf litter, root decomposition, and the protection of the soil surface from erosion.

• Alternate Wetting and Drying (AWD) in paddy: a water management technique in rice cultivation that, while primarily targeted at methane reduction, also affects soil carbon dynamics by changing the anaerobic soil conditions that drive organic matter decomposition.

How Is Soil Carbon Measured?

This is where soil carbon projects become technically complex, and where honest explanation is important.

Measuring soil organic carbon requires soil sampling: physically extracting soil cores from measured depths across a project area, and sending them to a laboratory for carbon analysis. The results are expressed as a percentage of carbon by weight of dry soil (e.g., 1.2% SOC) or as tonnes of carbon per hectare when combined with the soil bulk density.

The challenge is variability. SOC is not uniform across a field: it varies with soil type, texture, depth, existing vegetation cover, and prior management history. To get a statistically representative measurement of the average SOC across a project area, a significant number of samples are needed. For a 500-hectare project, this might mean 150 to 300 soil cores, sampled at multiple depths (typically 0–30cm and 30–100cm), analysed individually or composited by stratification.

This sampling cost, both in time and laboratory analysis fees, has historically been one of the biggest barriers to soil carbon projects at smallholder scale. Recent advances in remote sensing and near-infrared spectroscopy are reducing the cost of soil carbon measurement, but rigorous soil sampling remains expensive and time-consuming.

The Additionality Challenge in Soil Carbon

Every carbon market methodology requires that credited emission reductions or removals be 'additional', meaning they would not have occurred without the carbon project intervention. In soil carbon projects, this requirement is more complex than in other project types.

Consider a farmer who has been applying farmyard manure to their field for twenty years because their grandfather taught them to. If a carbon project comes along and offers to pay them for the soil carbon they are building, is that additional? The answer depends on whether the baseline, the amount of SOC that would have existed without the project, is correctly established.

If the farmer was already doing the practice before the project, the SOC from that practice is not additional. Only the incremental improvement attributable to the project intervention, perhaps an increase in the quantity of organic matter applied, or the addition of a cover cropping practice that was not previously used, generates additional credits.

This nuance is why soil carbon projects require careful baseline surveys and why the credited volume is often more conservative than the gross improvement in SOC might suggest.

The Permanence Question

Unlike trees, which continue to store carbon as long as they are standing, soil organic carbon is more dynamic: it can be released back to the atmosphere if practices change. A farmer who builds up SOC over five years through reduced tillage and compost application, and then reverts to deep tillage and residue burning, will lose much of that accumulated SOC relatively quickly.

Carbon market methodologies address this risk through permanence requirements, project commitments to maintain the practice for a defined minimum period (typically 20–50 years for soil carbon projects, which is longer than most agroforestry projects), and buffer pool contributions that insure against reversal risk.

The permanence requirement is the most demanding aspect of soil carbon projects for smallholder farmers. Committing to maintain a specific set of farming practices for two or three decades requires a level of certainty about the future of one's land and livelihood that many smallholders, facing climate uncertainty, economic pressures, and intergenerational change in farm management, may find difficult.

Where This Sits in Karimam's Project Portfolio

Karimam treats soil carbon as a secondary methodology layer in most of its current project designs, stacked on top of primary agroforestry (VM0047) projects, rather than as a standalone project type.

The reason is practical: the measurement costs for a standalone soil carbon project are difficult to justify at smallholder aggregated scale with current methodology requirements. But as a supplementary component of an agroforestry project, where the trees themselves are the primary sequestration mechanism and the improvement in soil carbon under the trees is an additional, modest co-benefit, soil carbon can be credibly documented with a reduced sampling burden.

As methodology technology matures, and particularly as remote sensing-based SOC measurement becomes more cost-effective, dedicated soil carbon projects at FPO scale in India will become increasingly viable. Karimam is monitoring these methodological developments closely, and anticipates that soil organic carbon will become a significant component of its project portfolio in the 2027–2030 period.

Soil organic carbon measurement methodology and sampling protocols follow IPCC Tier 2 guidance and applicable Verra VCS and ICM methodology requirements. All soil carbon estimates in Karimam project documentation are supported by laboratory-verified soil sample data.