Global Research Alliance N2O chamber methodology guidelines: Statistical considerations, emission factor calculation, and data reporting

Static chambers are often used for measuring nitrous oxide (N2O) fluxes from soils but statistical analysis of chamber data is challenged by the inherently heterogeneous nature of N2O fluxes. As N2O chamber measurements are commonly used to assess N2O mitigation strategies or to determine country-specific emission factors (EFs) for calculating national greenhouse gas inventories, it is important that statistical analysis of the data is sound and that EFs are robustly estimated. This paper discusses the challenges associated with statistical analysis of heterogeneous data and provides recommendations and guidance on how to address these, including assessing for normality and options for transforming data that follow a non-normal distribution. We also recommend minimum requirements for reporting of (meta) data of N2O studies to ensure that the robustness of the results can be reliably evaluated. This includes detailed information the experimental site, methodology and measurement procedures, gas analysis, data and statistical analyses, approaches to generate emission factors, as well as results of ancillary measurements. The reliability, robustness and comparability of soil N2O emissions data will be improved through i) application, and reporting, of more rigorous methodological standards by researchers, and ii) greater vigilance by reviewers and scientific editors to ensure that all necessary information is reported in scientific publications.