An automated time-integrating chamber system with offline gas analysis to monitor N2O fluxes on agricultural ecosystems

Static chambers are the predominating method for measuring N₂O emissions from agricultural ecosystems and thus provide the basis for deriving corresponding emission factors. In order to obtain representative N₂O emission values, long-term measurements (one to several years) are necessary that capture relevant short-term variations including diurnal cycles and pulse-like emissions after fertilizer applications or rainfalls. The latter is often a problem for the widely used manual chamber measurements that are typically applied in weekly or bi-weekly intervals. Fully automated chamber systems, on the other hand, can provide continuous measurements over longer time periods, but they are relatively expensive and usually require online and thus on-site gas analysis in the field. To overcome this problem, we constructed an automatic non-steady-state chamber system (ATIC) that accumulates air samples from four time points during the 15-min chamber closure in different gas bags. The chamber can be closed e.g. every four hours covering diurnal cycles as well a short pulse emission events. After typically one week, the bags with the accumulated samples (representing a time-averaged concentration increase) are brought to the lab for gas analysis. In this way, weekly time-integrated gas emission fluxes can be determined. The individual chamber systems can run on battery.

The ATIC systems were successfully applied in two field experiments covering more than two full years each. One experiment was performed on a permanent grassland and the other on a arable field with ley. In both cases weekly time integration and gas analysis intervals were used. We will show the setup of the system, the quality control of the data and the resulting N₂O emission time series. They showed e.g. that the N₂O emission from a grassland on peat soil was significantly reduced after coverage of the peat by a mineral soil layer. In the future, the system will also be used for analyzing the isotopic composition of the emitted N₂O.