Choosing the appropriate methodology to monitor soil organic carbon (SOC) in croplands: aligning methods with evolving monitoring reporting verification (MRV) frameworks

Monitoring soil organic carbon (SOC) has gained significant recognition, not only for national greenhouse gas inventories but also for voluntary carbon markets and agri-environmental policies. This has amplified the need for accurate, continuous, and cost-effective SOC stock monitoring from field to national scales. Consequently, methodological frameworks have emerged to address these diverse needs. They rely on measurement and/or modeling of the SOC, considering several complexities (Tiers 1, 2 and 3), combined or not with remote sensing. However, practical implementation guidelines for choosing the most suitable monitoring approach for specific contexts and purposes remain incomplete. Therefore, this study analyses current SOC monitoring methodologies for croplands and proposes a decision tree to help MRV stakeholders select the monitoring strategy considered most appropriate for their context. It confirmed that currently there are no fit-for-all-purposes method, while it recommends whenever possible, the use of measure–remeasure or parsimonious Tier 3 modeling approaches with Earth-Observation data assimilation. Indeed, the assimilation of biomass or proxies derived from remote sensing into those models allows better quantification of biomass restitution to the soil and improves model accuracy and scalability at low cost. Finally, we highlight possible improvements in the different monitoring approaches and key challenges that still need to be overcome.