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The capacity and long-term stability of soil organic carbon (SOC) are governed by its composition. SOC is commonly conceptualized as two major pools: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). While POC represents a labile fraction that responds rapidly to management and environmental change, MAOC is stabilized through physical and chemical associations with soil minerals, resulting in substantially longer turnover times.Although the concept of carbon saturation has been widely discussed, empirical information on the spatial distribution of POC and MAOC contrasting pedo-climatic conditions remains limited, particularly at regional scales. As a result, the extent to which agricultural soils are able to further accumulate SOC under different environmental settings is still poorly constrained.In this study, we investigate the distribution of POC and MAOC in cropland soils across Czechia by combining physical size fractionation method with digital soil mapping. Soil samples from a nationwide sampling network are separated to quantify POC and MAOC stocks down to 0.6 m soil depth. These data will be integrated with spatially explicit, high-resolution environmental covariates, including climate variables, soil properties, and terrain attributes, to model the distribution of carbon fractions across 25 major pedo-climatic zones.These results will provide insights into the current carbon saturation of cropland soils under different pedo-climatic conditions. This further allow identification of regions with a high potential for additional carbon sequestration, as well as areas where SOC stocks may already be constrained by mineralogical or climatic limitations. The expected outcomes will contribute to a process-based understanding of SOC stabilization at the landscape scale and provide a basis for region-specific soil carbon management and climate-mitigation strategies.