Soil carbon glossary

Soil organic carbon(SOC)

The carbon held in soil organic matter — decomposing plant, microbial, and animal material. It is the soil carbon pool most influenced by land management and the focus of agricultural carbon projects.

Soil inorganic carbon(SIC)

Carbon stored in soil minerals such as carbonates. It changes over much longer timescales than SOC and is generally not the target of soil carbon crediting.

Measurement, reporting and verification(MRV)

The system used to quantify, document, and independently verify a project's carbon outcomes. Credible SOC MRV combines soil sampling, remote sensing, and modelling with quantified uncertainty.

Project Design Document(PDD)

The core document describing a carbon project's baseline, additionality, quantification method, and monitoring plan, which validators and registries assess.

Additionality

The requirement that emission reductions or removals would not have happened without the carbon project — so credits represent genuine, extra climate benefit.

Permanence and reversal

Permanence is how durably carbon stays stored; reversal is its release back to the atmosphere (for example if practices revert). Standards manage reversal risk with buffer pools and monitoring.

Baseline

The reference scenario of carbon stocks and emissions that would occur without the project. Credited change is measured against this baseline.

Measure-and-model

A quantification route that calibrates a process model (such as RothC, CENTURY, or DNDC) against measured soil samples to estimate SOC change across areas and years.

Measure-and-remeasure

A quantification route that directly measures SOC stocks at the start and re-measures on a defined cycle, quantifying change empirically.

Equivalent soil mass(ESM)

A correction that compares soil carbon on a fixed soil-mass basis rather than a fixed depth, avoiding false changes caused by differences in bulk density.

VM0042

Verra's Improved Agricultural Land Management methodology for crediting GHG benefits, including soil organic carbon, from cropland and grassland practice change.

RothC

A widely used, relatively simple process model of soil organic carbon turnover, commonly applied in measure-and-model quantification.

DNDC

The DeNitrification-DeComposition model, a process model that simulates soil carbon and nitrogen dynamics, including greenhouse-gas emissions, in detail.

CENTURY

A process model of soil organic matter and nutrient dynamics suited to longer-term simulations of SOC change.

ICVCM Core Carbon Principles(CCP)

Integrity Council for the Voluntary Carbon Market benchmarks defining high-quality carbon credits. The first sustainable-agriculture methodologies have been approved against them.

Tier 3 modeling

The most detailed IPCC estimation approach, using site-specific process models — increasingly with Earth-observation data assimilation — rather than default factors.

Insetting

Reducing or removing emissions within a company's own supply chain (for example funding soil carbon practices on supplying farms), as opposed to buying external offsets.

Removal vs reduction

A removal draws CO₂ out of the atmosphere and stores it (such as new soil carbon); a reduction avoids emissions that would otherwise occur. Both can be credited but are distinct claims.

Durability

How long stored carbon remains out of the atmosphere. Soil carbon is durable but reversible, so durability is managed through monitoring and reversal-risk rules.

New to the topic? Start with What is soil organic carbon?