Microcosm Study with Continuous Dynamic Monitoring of Nitrous Oxide Diffusion and Reduction in Agricultural Soil at Variable Moisture

Nitrous oxide (N 2 O) production and consumption occur concomitantly in the soil and their accurate quantification as the gas diffuses in situ under high background concentration of atmospheric dinitrogen remains largely elusive. This study designed an analytical and reliable approach for continuous and dynamic monitoring of N 2 O in the laboratory. The approach is based on passive diffusion and reduction of standard N 2 O gas through undisturbed soil columns and was tested at 30, 50, 60 and 80% water filled pore space (WFPS). The N 2 O fluxes were followed by an automated system of quantum cascade laser coupled with cavity enhanced laser absorption spectroscopy continuously for 22 days and residual N 2 O in the system was quantified by a mass balance approach. A semi-physical model was used to quantify the reduction of N 2 O diffusing upward through the soil layers and the importance of the soil physical properties and metagenomics measured at the start and the end of the experiment.Residual fluxes were little and significantly higher at 50 and 60% WFPS, being the most suitable conditions for N 2 O production, compared to 30 and 80% WFPS. The total recovery of N 2 O followed the order 30>50≈60> 80% WFPS with corresponding share of 39, 26, 23 and 13% from the total N 2 O injected, which clearly pointed on 80% WFPS with the largest reduction of N 2 O to N 2 . The results analytically confirmed the rather argued scientific opinion that soil moisture have a dominant effect on N 2 O diffusion and reduction in the soil, with significant correlation (R 2 >0.8). During the experiment, 60% WFPS was the most conductive for N 2 O emission, while the diffusion flux was the largest at 30% WFPS