Investigating the stomatal, cuticular and soil ammonia fluxes over a growing tritical crop under high acidic loads
Ammonia concentration and fluxes were measured above a growing triticale field 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 point Cc was around 1.5 μg NH 3 m −3 on average. The canopy emission potential Γ c ( Cc 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.