Use of silicone tubes as a simple method to measure in situ soil gas N₂O concentrations and fluxes

Chamber method, which was used as a regular way to measure N2O fluxes from soils, has the disadvantages on sampling in situ soil-derived N2O with high concentration, monitoring N2O fluxes under all weather conditions and studying the behaviors of N2O in soil profile. The possibility of using silicone tubes to sample in situ soil gas was tested by measuring the diffusivity of standard N2O gas through the silicone tube walls. Field plots were under treatments of NH+4、NO-3 and NO-3 plus glucose, with four randomly arranged replicates. Silicone tubes and sampling chambers were buried under soil surface with different depths. In situ collection of soil N2O with high concentration and the efficiency of monitoring the concentration and fluxes of N2O were compared, as the silicone tube and traditional chamber had different sensitivity to N2O variation in soil. Results revealed that it took only 2.9 hours for N2O in the silicone inner space to reach 95% equilibrium with the surrounding atmosphere, which was fast enough to satisfy regular sampling interval. The silicone tubes method had the advantage over chamber method in collection of soil-derived N2O with high concentration and the collected sample showed clear trends concerning N2O concentration over time. The temporal variation of N2O emissions calculated by different methods showed significantly positive correlations, while the silicone tube method gave lower values. The agreement of two data sets depended on the matching of the site of sampling and N2O production. It is recommended to bury horizontal silicone tube at surface soil layer for N2O flux monitoring or at different soil depths to investigate the spatial and temporal variation of N2O behavior in soil profile.