A five-stage protocol for systematic measuring soil carbon and greenhouse gas fluxes in complex estates

•Background and Aims: Plant-soil interactions are critical in governing soil carbon (C) stocks and greenhouse gas (GHG) fluxes, but they vary significantly across land uses, soil types, and soil management practices. Finding a potential intervention that could enhance soil C and GHG fluxes relies on reliable baseline data that can capture these variations. Complex estates, characterised by such heterogeneous conditions, require standardised protocols to ensure reproducibility and comparability across sites. •Methods: This study introduces a five-stage protocol for systematically measuring and potentially monitoring soil C stocks (including organic and inorganic forms) and GHG fluxes. The protocol is exclusively designed for "Time-Zero" (T=0) baseline assessments and the strategic selection of sampling sites. However, it also offers a consistent and robust adjustment of the protocol for long-term soil sampling and GHG flux measurements (i.e. monitoring purposes). The approach was tested at RAF Leeming, a Royal Air Force base (500 ha) located in Yorkshire, UK, with varied land uses, soil types, and management practices. •Results: The protocol provided a rigorous, reproducible and adaptable framework for obtaining robust baseline data. It also facilitated the quantification of soil C and GHG fluxes, demonstrating the value of a standardised approach to avoid potential under- or overestimation. Additionally, the proposed protocol proved to be useful to guide site-specific interventions by ensuring that relevant factors, such as plant and soil interactions and environmental covariates, are integrated to enhance comparability across space and time. The results also reinforce the scalability of the protocol, with potential applications across a range of complex estates, including urban areas, military installations, airports, and other managed landscapes. •Conclusions: The proposed protocol enables standardised, transparent soil C and GHG flux monitoring to meet internationally accepted standards. We advocate for its broad implementation across estates with varying land uses and soil characteristics to support sustainable soil management and climate mitigation efforts.