Investigating the stomatal, cuticular and soil ammonia fluxes over a growing tritical crop under high acidic loads

Abstract. Ammonia concentration and fluxes were measured above a growing triticalefield for two months during May and June 2010 at the NitroEurope crop site in Grignon (Fr-Gri) near Paris, France. The measurement campaign started 15 days following a 40 kg N ha −1 application of an ammonium nitrate solution. A new mini-wedd (Wet Effluent Denuder) flow injection analyser with three channels (ROSAA, RObust and Sensitive Ammonia Analyser) was used to measure NH 3 fluxes using the aerodynamic gradient method. The measured ammonia concentrations varied from 0.01 to 39 μg NH 3 m −3 and were largely influenced by advection from the nearby farm. The ammonia fluxes ranged from –560 to 220 ng NH 3 m −2 s −1 and averaged –29 ng NH 3 m −2 s −1 . During some periods the large deposition fluxes could only be explained by a very small surface resistance, which may be partly due to the high concentrations of certain acid gases (HNO 3 and SO 2 ) observed in this suburban area. Ammonia emissions were also observed. The canopy compensation pointC c was around 1.5 μg NH 3 m −3 on average. The canopy emission potential Γ c ( C c normalised for the temperature response of the Henry equilibrium) decreased over the course of the measurement campaign from Γ c = 2200 to Γ c = 450, the latter value being close to the median stomatal emission potential (Γ s ) and lower than the median ground emission potential (Γ g ) for managed ecosystems reported in the literature. The temporal dynamics of the measured NH 3 flux compared well with the Surfatm-NH 3 model using fitted parameters. The subjectivity of the model fitting is discussed based on a sensitivity analysis.