Global Research Alliance N₂O chamber methodology guidelines: Recommendations for deployment and accounting for sources of variability

Abstract

Adequately estimating soil nitrous oxide (N 2 O) emissions using static chambers is challenging due to the high spatial variability and episodic nature of these fluxes. We discuss how to design experiments using static chambers to better account for this variability and reduce the uncertainty of N 2 O emission estimates. This paper is part of a series, each discussing different facets of N 2 O chamber methodology. Aspects of experimental design and sampling affected by spatial variability include site selection and chamber layout, size, and areal coverage. Where used, treatment application adds a further level of spatial variability. Time of day, frequency, and duration of sampling (both individual chamber closure and overall experiment duration) affect the temporal variability captured. We also present best practice recommendations for chamber installation and sampling protocols to reduce further uncertainty. To obtain the best N 2 O emission estimates, resources should be allocated to minimize the overall uncertainty in line with experiment objectives. Sometimes this will mean prioritizing individual flux measurements and increasing their accuracy and precision by, for example, collecting four or more headspace samples during each chamber closure. However,

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

“…Charteris et al. (2020) provide recommendations for experimental design and deployment of chambers to reduce the uncertainty associated with the spatial, temporal, and experimental variability in N 2 O fluxes. These authors also discuss the use of power analysis to determine the required number of replicates.…”

“…Charteris et al. (2020) recommends that, as a minimum, N 2 O measurements should be taken at least twice per week when higher emissions are likely to be occurring, and at even higher intensities around events (e.g., rainfall, fertilization, cultivation). When conditions are conducive to near‐zero N 2 O fluxes (e.g., in dry or cold soils), weekly or biweekly sampling may be adequate.…”

Global Research Alliance N2O chamber methodology guidelines: Introduction, with health and safety considerations

“…All papers provide some refinement from the original chapters to include the latest literature and understanding of topics, but three chapters have undergone more extensive revision. The “deployment” paper (Charteris et al., 2020) now includes a more thorough discussion and analysis of the sources of variability associated with N 2 O emissions. The “flux calculation” paper (Venterea et al., 2020) now includes a thorough analysis of different flux calculation (FC) methods and decision trees summarizing recommendations on procedures for screening data based on analytical error and minimum detectable fluxes, and for selecting the most appropriate FC method.…”

“…Charteris et al. (2020) provide a comprehensive set of recommendations on three key topics: (a) addressing spatial variability; (b) addressing temporal variability; and (c) practical and experimental aspects. The aspects relating to spatial variability include site selection, experimental design structure, chamber coverage and size, pre‐experiment measurements to examine underlying flux variability, chamber placement to account for soil or crop features or gradients, and treatment application.…”

“…Any decisions on balancing limited resources to achieve the best possible (most accurate) results should, therefore, take into account the magnitude of the uncertainty associated with each step of the N 2 O chamber methodology and the relative impact each of these uncertainties has on calculating cumulative emissions and emission factors. Two articles included in this special section discuss issues related to balancing resources in more detail and provide some tools for its assessment (Charteris et al., 2020; Venterea et al., 2020).…”