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 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 NH₃ fluxes using the aerodynamic gradient method. The measured ammonia concentrations varied from 0.01 to 39 μg NH₃ m⁻³ and were largely influenced by advection from the nearby farm. The ammonia fluxes ranged from –560 to 220 ng NH₃ m⁻² s⁻¹ and averaged –29 ng NH₃ 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 (HNO₃ and SO₂) observed in this suburban area. Ammonia emissions were also observed. The canopy compensation point <i>C</i>_c was around 1.5 μg NH₃ m⁻³ on average. The canopy emission potential &Gamma;_c (<i>C</i>_c normalised for the temperature response of the Henry equilibrium) decreased over the course of the measurement campaign from &Gamma;_c = 2200 to &Gamma;_c = 450, the latter value being close to the median stomatal emission potential (&Gamma;_s) and lower than the median ground emission potential (&Gamma;_g) for managed ecosystems reported in the literature. The temporal dynamics of the measured NH₃ flux compared well with the Surfatm-NH₃ model using fitted parameters. The subjectivity of the model fitting is discussed based on a sensitivity analysis.