Nitrous Oxide Chamber Methodologies – Evolving Issues and Collection of Ancillary Data to Enhance Flux Interpretations.

For the last 30 years, static chambers have been the most commonly used method for measuring N₂O fluxes from agricultural soils, as they are relatively inexpensive, versatile and easy to adopt. Consequently, much of the knowledge that underpins the estimation of national agricultural N₂O emission inventories is based on chamber measurements. Nitrous oxide chamber methodologies rely on measuring the accumulation of N₂O within a chamber placed on the soil surface. Multiple chambers are deployed over a given time period and sampled at a given sampling frequency to determine spatially and temporally integrated N₂O emissions. Chamber design, deployment and data analysis all have the potential to bias results or third-party interpretation of those results. This limits inter-study comparisons and assessment of the uncertainty associated with the results. The international science community recognised the need for standardised guidelines on the use of chambers – and associated data reporting – for measuring N₂O emissions from agricultural soils. In 2011/12, the New Zealand Government, in support of the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases, funded an international collaboration to develop the Nitrous Oxide Chamber Methodology Guidelines. This paper provides a summary of ‘agreed minimum standards’ and ‘site or system specific requirements’ for each of the key components of chamber methodologies. It then focuses on aspects of the methodology for which there was no consensus (‘evolving issues’). These evolving issues include: balancing resources between carefully measuring individual fluxes and increasing chamber replication and frequency of sampling to account for variability, the type of ancillary data to be collected (e.g. soil parameters), and the method of integration of flux measurements. Understanding the size of the uncertainties of each step of the chamber measurement approach will be of critical importance for balancing (limited) resources to enhance interpretation of flux measurements.