A Comparison of Manual and Automated Flux Chamber Measurements to Determine Seasonal Nitrous Oxide Emissions: How Much Data Is Enough?.

Most field studies requiring nitrous oxide (N₂O) emissions measurements employ flux chambers because of their affordability and flexibility. When planning a greenhouse gas sampling campaign using the chamber-based approach, researchers are faced with a multitude of decisions regarding the best allocation of their limited resources. Practical considerations constrain both the total number of samples that can be collected in the field and the number of samples that can be processed in the laboratory in a timely fashion. Most N₂O sampling protocols call for the collection of multiple, equally spaced time-points, and though this approach will no doubt increase the accuracy of the daily flux estimate, it also dramatically increases the number of gas samples to be analyzed. Because only a limited number of samples can be collected, this invariably means that researchers must compensate by including fewer numbers of treatments and/or replications, or by decreasing sampling frequency. In this talk, we will discuss issues associated with deciding “how much data is enough” to accurately estimate seasonal N₂O emissions. Using manually sampled gas flux chambers (with gas chromatographic analysis of discrete gas samples collected during chamber deployment) and automated gas flux chambers interfaced to an FTIR gas analyzer for semi-continuous flux measurements in the field, we examined the impact of sampling frequency, as well as the influence of utilizing single versus multiple time-point flux estimates to calculate cumulative N₂O loss from field plots receiving varying amounts of fertilizer N. In this talk, we will discuss the results obtained during three field seasons (2014–2016).