Comparing soil organic carbon stock estimation methods for agricultural stony soils in Ireland: a regression-based approach

Despite the importance of national-scale soil organic carbon (SOC) monitoring, current measurement approaches often lack reliability. Research has primarily focused on global standardisation, but there remains a critical need for methods that account for soil heterogeneity while ensuring logistical feasibility for large-scale monitoring. This study addresses this gap by comparing two SOC stock assessment methods, Equivalent Soil Mass (ESM) and Fixed Depth (FD), using 1184 soil samples spatially distributed in the southeast of Ireland. A linear regression model incorporating stoniness and depth was developed to improve ESM-based estimations. Results indicate that ESM, when adjusted for these factors, provides a reliable estimate of SOC stocks and can substitute FD under most conditions. Given its ease of implementation compared to FD and its ability to capture landscape variability, ESM is recommended for large-scale SOC monitoring. However, a hybrid approach may be needed in soils with extreme stoniness. These findings support integrating ESM into national carbon monitoring frameworks to enhance the accuracy of national SOC inventories.