Soil organic carbon is essential to healthy, productive soils, but measuring changes in soil carbon can be challenging. A Hughes Center-funded study of 15 Maryland farms examined how well soil carbon models estimate existing carbon stocks and changes over time.
The principal investigators for the project included Dr. Gurpal Toor of the University of Maryland College of Agriculture and Natural Resources and Dr. Keith Paustian of the Colorado State University. Dr. Suzanne Dorsey, deputy secretary of the Maryland Department of the Environment, along with Emileigh Lucas of UMD and Elizabeth Ellis of CSU, also contributed.
Researchers compared direct soil measurements with estimates from USDA’s free COMET-Farm tool and a field-specific DayCent model. The study found that COMET-Farm was more useful for comparing potential changes under different management practices than for measuring the amount of carbon currently stored in a field. Field-specific modeling improved estimates, highlighting the importance of including practices such as drainage and manure application history in the calculation, but the DayCent model required more experience to use than the user-friendly COMET-Farm model.
The research provides practical guidance for farmers and agricultural advisors on using soil carbon models, interpreting results and determining when direct soil sampling is needed to support soil health and conservation decisions.
A practical guide for farmers and crop advisors, written by Dr. Toor and Dr. Dorsey, is available here.
Soil Carbon and Soil Health in Maryland Agriculture
In this webinar hosted in September 2026, Dr. Gurpal Toor of the University of Maryland College of Agriculture and Natural Resources, along with Maryland Department of the Environment Deputy Secretary Suzanne Dorsey, discusses a Hughes Center-funded study on measuring soil organic carbon on Maryland farms. Dr. Toor shares findings from a study of 15 working Maryland farms, explores factors influencing soil carbon levels and evaluates the USDA’s COMET-Farm model. The presentation also covers soil sampling methods, carbon sequestration and cost considerations of carbon measurement programs.