Farming practices such as cover cropping, reduced tillage and improved grazing can store carbon in agricultural soils.
What farmers change
Soil carbon projects pay farmers to adopt practices that add organic matter to soil or reduce its loss. Examples include cover crops, reduced or no tillage, rotational grazing and the use of compost. Carbon accumulates over several years, and some of it can be lost again if the practice stops.
The measurement problem
Soil carbon changes slowly and varies widely across a single field, so measuring it precisely is difficult. Projects combine soil sampling with modelling, and many methodologies require repeated sampling over many years. Buyers should look at how much uncertainty is built into the credit numbers.
Permanence
Soil carbon is reversible. If a farm returns to intensive tillage, stored carbon can be released. Contracts with farmers usually run for a fixed term and include commitments to maintain practices, and registries may hold back a buffer.
Questions to ask before you rely on these credits
- How often is soil sampled, and what depth is measured?
- What happens if a farmer stops the practice during the contract term?
- Is the uncertainty in the carbon estimate reflected in the number of credits issued?