Integrated Use of the Inverse Dispersion Technique and the Chamber Method to Determine N2O and NH3 Emissions from Agricultural Soils.

Nitrous oxide (N₂O), one of strong greenhouse gases (GHGs) with the global warming potential (GWP) value of 300, emitted from agricultural soils is mainly from the use of inorganic nitrogen fertilizer (e.g., anhydrous ammonia). The fluxes of GHGs emitted from soils are continuous, and dynamics and the soil heterogeneities result in the episodic gas emissions. The chamber methods are subject to the inherent limitations that substantially lead to the uncertainties in the estimations of GHG emissions, such as the small footprint (~ 0.6 m²) and the wild sampling interval (~ once a week). Open-path techniques combined with the inverse dispersion method is capable of acquiring the “real-time” data at a relatively high temporal resolution (minutes) and provides the gas emissions with a great spatial representative (> 100 m²). In this study, we determined N₂O emissions from the continuous maize fields with different field managements (i.e. Chisel plow vs. No-till, and Full (200 kg NH₃-N/ha) vs. Split (100+100 kg NH₃-N/ha) N applications in the Fall and Spring) using the chamber measurement and the open-path method. The results showed that the full application led to the higher N₂O emissions compared with the split application, and the cumulative N₂O emissions within the first 20 days after NH₃ applications indicated that the full N application during the Spring tended to cause higher N₂O emissions than the application during the Fall (Spring application: 10 kg ha^-1 vs. Fall application: 7.1 kg ha^-1). Furthermore, the open-path method can detect the diurnal fluctuations of N₂O emissions which were corresponding to the diurnal changes of soil temperature and wind speed, and the chamber method over underestimated N₂O emissions compared to the open-path method during the daytime because of the lack of considerations of turbulence effect on gas emissions.