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

Non-steady state (NSS) chamber techniques have been used for decades to measure nitrous oxide (N2O) fluxes from agricultural soils. These techniques are widely used because they are relatively inexpensive, easy to adopt, versatile and adaptable to varying conditions. Much of our current understanding of the drivers of N2O emissions, efficacy of mitigation practices, as well as estimations of agricultural N2O emission inventories, are based on using NSS chambers. While easy to adopt, use of NSS chambers requires decisions regarding multiple methodological aspects including chamber materials and geometry, sample replication, timing and frequency, sample analysis, use of ancillary information, and data analysis and statistical methods, each of which may significantly impact the results. Variation in these methodological details can lead to challenges in comparing results between studies and assessment of reliability and uncertainty. Therefore, the New Zealand Government, in support of the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases (GRA), funded an international project to develop standardised guidelines on the use of NSS chambers. Building on these initial guidelines, an international team of scientists have since refined them based on the most up to date knowledge and method developments. This introductory paper summarizes a collection of papers, comprising this special section of the Journal of Environmental Quality, that represent the revised guidelines. Each article summarises existing knowledge and provides guidance and recommendations for key aspects, including design, deployment, sample collection, storage and analysis, automated chambers, flux calculations, statistical analysis, emission factor estimation and data reporting, modelling approaches, and guidelines for ‘backfilling’ missing measurements. In addition, health and safety (H&S) considerations are included in this introductory paper. Each paper defines minimum requirements; however, these are not meant to be highly prescriptive, but instead to provide researchers with guidance on best practice and factors that need to be considered.