Temporal integration of soil N₂O fluxes: validation of IPNOA station automatic chamber prototype

The assessment of nitrous oxide (N₂O) fluxes from agricultural soil surfaces still poses a major challenge to the scientific community. The evaluations of integrated soil fluxes of N₂O are difficult owing to their lower emissions when compared with CO₂. These emissions are also sporadic as environmental conditions act as a limiting factor. A station prototype was developed to integrate annual N₂O and CO₂ emissions using an automatic chamber technique and infrared spectrometers within the LIFE project (IPNOA: LIFE11 ENV/IT/00032). It was installed from June 2014 to October 2015 in an experimental maize field in Tuscany. The detection limits for the fluxes were evaluated up to 1.6 ng N-N₂O m² s^-1 and 0.3 μg C-CO₂ m² s^-1. A cross-comparison carried out in September 2015 with the "mobile IPNOA prototype"; a high-sensibility transportable instrument already validated provided evidence of very similar values and highlighted flux assessment limitations according to the gas analyzers used. The permanent monitoring device showed that temporal distribution of N₂O fluxes can be very large and discontinuous over short periods of less than 10 days and that N₂O fluxes were below the detection limit of the instrumentation during approximately 70% of the measurement time. The N₂O emission factors were estimated to 1.9% in 2014 and 1.7% in 2015, within the range of IPCC assessments.