The short answer. The words used about soil carbon come from soil science, statistics, carbon markets and farm policy, and the same word can mean different things in each. This glossary explains the terms farmers, buyers and project developers meet most often, in plain English, and links to the guide that goes further.
Last reviewed September 2026.
Soil and measurement
Soil organic carbon (SOC)
The carbon held in the organic part of the soil: decomposed plant and animal residues, living organisms and the substances they make. It governs structure, how water gets in and is held, and how nutrients are made available to the crop. More in what soil organic carbon is.
Soil organic matter (SOM)
The material in the soil that came from living things. Organic carbon is the carbon within it, and it is the carbon that is measured when you want to track what your management is doing to the soil.
SOC concentration
The share of a soil sample that is organic carbon, as a percentage, as the laboratory reports it.
SOC stock
The amount of organic carbon in the soil across an area, in tonnes of carbon a hectare. It is calculated from the concentration, the bulk density of the soil and the depth sampled, and it is the figure that shows whether a field is gaining or losing carbon.
Bulk density
The dry weight of soil in a given volume, in grams per cubic centimetre. It is needed to turn a carbon concentration into a carbon stock.
Equivalent soil mass
A way of comparing carbon stocks on the same mass of soil rather than the same depth, so that a change in bulk density, for example after a change in cultivation, is not mistaken for a change in carbon.
Dry combustion
A laboratory method that burns a soil sample at high temperature and measures the carbon it releases directly. Every result we report is anchored to dry combustion analysis in a laboratory accredited to ISO/IEC 17025.
Loss on ignition (LOI)
A method that estimates organic matter from the weight a sample loses when it is heated. A useful rough guide, but not precise enough to measure a change in carbon stock. The methods are compared in soil carbon testing in the UK.
Baseline
The first measurement of your fields. Every later round is measured the same way, at the same point in the year, and compared with it. More in the soil carbon baseline.
Monitoring round
One annual measurement after the baseline, sampled in the same autumn-winter window, so the difference between rounds is a change in the soil rather than the time of year.
Stratification
Dividing land into groups that are alike before sampling, by area or by zone, so that fewer samples give a more reliable answer. More in soil sampling for soil carbon.
Composite sample
Several soil cores combined into one sample for the laboratory, typically 9 to 12 under our methodology.
Sentinel-2
The European Copernicus satellite mission whose imagery our AI ties to laboratory results, at a value every 10 metres, or 100 mapped values a hectare.
SBI number
The Single Business Identifier the Rural Payments Agency gives a farm business in England. It identifies the holding and its registered land parcels, which is why a quote can be written from your SBI number and your hectares alone.
Accuracy and uncertainty
Uncertainty
How far a result could be from the true value. No measurement is exact, so every result we report carries its uncertainty. More in accuracy stated.
Validation samples
Samples held back from the AI and used only to test it, so its error is measured on data it never saw.
Mean absolute percentage error (MAPE)
The average size of the difference between predicted and measured values, as a percentage. Our methodology uses it, measured on validation samples, to set the deduction for uncertainty.
Uncertainty deduction
The part of a measured gain in soil carbon taken off to allow for the error, before any credits are calculated.
Minimum detectable difference
The smallest change in soil carbon a sampling design can reliably detect. It depends on how many samples are taken and how much the soil varies.
Carbon credits and markets
Tonnes of carbon dioxide equivalent (tCO2e)
The common unit for greenhouse gases. A tonne of carbon stored in the soil is 3.67 tonnes of carbon dioxide.
Sequestration
Carbon taken from the atmosphere and stored, here in the soil.
Carbon removal
Greenhouse gas taken out of the atmosphere and stored. A soil carbon credit is a removal. More in removal and avoidance credits.
Emission reduction
Emissions prevented that would otherwise have happened, sometimes called avoidance. A different kind of result from a removal, and usually a different kind of credit.
Carbon credit
A tradeable certificate for one tonne of carbon dioxide equivalent removed or reduced, issued on a registry. With Ecometric, credits are issued for each tonne sequestered after greenhouse gas emissions are deducted. More in soil carbon credits for UK farmers.
Insetting
Reducing or removing emissions inside a company’s own supply chain, for example with credits from the farms it buys from.
Offsetting
Buying credits from outside a company’s supply chain to compensate for its emissions.
Additionality
The test that the carbon would not have been removed or reduced without the project.
Permanence
How long removed carbon stays stored. Soil carbon can be lost again, which is why credited projects are monitored and hold a buffer.
Reversal
Carbon that was credited and is later lost from the soil.
Buffer pool
A share of credits held back as insurance against reversals. Under our methodology, 20% of credits go into the buffer and 80% can be sold.
Leakage
Emissions or production pushed elsewhere by a project. Under our methodology, leakage linked to lost yield is deducted along with the farm’s emissions.
Double counting
The same tonne claimed more than once, by two buyers, two schemes or two inventories. It damages the value of every credit involved.
Carbon registry
The organisation that records projects and issues, tracks and retires credits, so each tonne can only be used once. Our methodology is published on the Regen Registry.
Retirement
Taking a credit out of circulation when it is used to make a claim, so it cannot be sold again.
Methodology
The published rules for how carbon is measured, calculated and reported for a type of project. Our methodology is public.
Credit class
A registry’s framework for a type of credit, setting which methodologies and projects can issue credits under it.
Project developer
The organisation that designs and runs a carbon project and takes it through registration and verification. More in for project developers.
Carbon credit rating
An independent opinion, usually a letter grade from AAA to D, on how likely a credit or project is to deliver the tonne it claims. BeZero Carbon and Sylvera are the best-known agencies. More in carbon credit ratings explained.
Core Carbon Principles (CCP)
The Integrity Council for the Voluntary Carbon Market’s ten principles for high-quality carbon credits. The CCP label shows that both the crediting programme and the type of credit have been approved against them.
VCMI Claims Code
Guidance from the Voluntary Carbon Markets Integrity Initiative on the claims a company can make when it uses carbon credits alongside its own emission cuts.
Standards and reporting
MRV
Measurement, reporting and verification: how a carbon result is quantified, reported and independently checked.
Validation and verification body (VVB)
An independent organisation that checks a project’s design against the rules and verifies the results it reports. More in how carbon credits are verified.
ISO 14065
The international standard for bodies that validate and verify environmental information, including greenhouse gas statements.
ISO 14064-2
The international standard for quantifying, monitoring and reporting greenhouse gas reductions and removals at project level.
ISO/IEC 17025
The international standard for the competence of testing and calibration laboratories.
IPCC tiers
Levels of detail for calculating greenhouse gas emissions. Tier 1 uses default factors, Tier 2 uses factors specific to a country or region, and Tier 3 uses models or detailed measurement. Emissions under our methodology are calculated to Tier II or higher.
Scope 3 emissions
The indirect emissions in a company’s value chain, including those from the farms that supply it.
GHG Protocol Land Sector and Removals Standard
The GHG Protocol standard for how companies account for land emissions and removals, published in January 2026 and in effect from 1 January 2027. Removals can only be reported with traceable, field-specific data, a stated uncertainty and ongoing monitoring.
SBTi FLAG
The Science Based Targets initiative’s guidance for forest, land and agriculture. Companies in land-intensive sectors, or whose land-related emissions are 20% or more of their total, set separate targets for them, and purchased offsets cannot count towards those targets.
Carbon footprint
An estimate of the greenhouse gases a farm or product emits, worked out in a calculator from records. In farming it is often called a carbon audit. More in farm carbon audit or soil carbon measurement.
PAS 2050
A British specification for assessing the life cycle greenhouse gas emissions of goods and services. Carbon audits for Scotland’s Whole Farm Plan must be aligned to it, or be part of a UK supply chain contract.
Farm schemes and rules
Sustainable Farming Incentive (SFI)
England’s scheme that pays farmers for actions that benefit the environment, including actions on the soil such as no-till, cover crops and herbal leys. More in SFI26 soil actions and soil carbon.
Farming Rules for Water
Rules in England to prevent water pollution from farming. If you apply manure or fertiliser to cultivated land, your plans must use soil test results no more than five years old. More in soil health testing in the UK.
Whole Farm Plan
Scotland’s requirement for farmers and crofters claiming support payments to complete audits and plans, including a carbon audit and soil analysis that now includes soil carbon.
Sustainable Farming Scheme (SFS)
The farm support scheme in Wales from 1 January 2026, which includes soil testing with soil organic matter and a farm level carbon baseline.
Something missing, or a term you have met that is not here? Tell us, and if it is about your own fields, send us your SBI number and your hectares and we will send a written quote within two working days.
Part of our guide to soil carbon measurement for farms. Related: how soil carbon is measured · accuracy stated · soil carbon credits for UK farmers
