On-farm soil organic carbon sequestration potentials are dominated by site effects, not by management practices

Although conservation agriculture practices evidently facilitate the build-up of soil organic carbon (SOC), the sequestration potential of arable soils is strongly mediated by edaphic attributes; so far, their interplay is not well understood. Deciphering these drivers is however important to correctly estimate SOC storage potentials in arable soils and to derive effective strategies for the implementation of successful measures. By using an on-farm approach, we conducted a pairwise comparison of 21 conventional and highly innovative 'pioneer' farms across a wide range of arable soil types and evaluated the leverage of site attributes and management practices such as crop diversity, reduced tillage, organic fertilization, cover cropping and inter cropping on the SOC sequestration potential.While most pioneer management practices proved beneficial for the sequestration of SOC - particularly cover cropping and crop diversity - our results clearly show that soil texture was the most significant shaping factor. Coarse-textured soils had a significantly higher potential for SOC accrual compared to medium- and fine-textured soils. The initial SOC content also had a significant effect on prevalent sequestration potentials. Based on the fact of a clear predominance of natural site conditions over management impacts in enhancing SOC storage of arable soils, we call for a critical discussion of carbon farming schemes. As similar efforts and costs of implementing carbon farming measures will have distinctive carbon gains, dependent on environmental constraints beyond farmers' influence, we advocate for strategies harmonizing both activity- and results-based approaches to maximize the ecological effectiveness and the spatial dissemination of soil health innovations. Carbon farming schemes thus need reconsideration within the state-of-the-art scientific framework of carbon saturation behav- iour in order to properly account for biophysical constraints when formulating soil-related climate change mitigation policies.