Continuous, Long-Term, Field-Integrated Measurements of N2O Emissions Using Static Chambers and the Flux Gradient Method over a Winter Wheat Field in the Inland Pacific Northwest.

Agriculture is a large source of the greenhouse gas nitrous oxide (N2O) , but emissions of the gas are difficult to measure due to the high degree of spatial and temporal variability. To determine the N2O source strength of wheat cropping systems in the Inland Pacific Northwest, continuous measurements of emissions are required over multiple crop years. Micrometeorological flux techniques such as eddy covariance and flux gradient can theoretically provide robust monitoring at the field scale, but in practice background N2O emissions are too small to be detected by these flux techniques. Automated static chambers are a reliable way to continuously monitor emissions, but the high degree of spatial variability in N2O emissions makes upscaling to field-scale estimates difficult. Furthermore, high-precision real-time N2O analyzers are expensive, so using multiple methods simultaneously can be cost prohibitive. The research presented here integrates an array of automated static chambers with flux gradient measurements using just one N2O analyzer per site to optimize monitoring of N2O at two sites in Eastern Washington. The sites have similar climates and crop rotations, the main difference is that one is operated under conventional tillage and the other is a no tillage field. Results from the robust N2O monitoring will thus provide a benchmark for N2O emission rates from this region and also allow for evaluation of the impact of tillage type on N2O emissions.