The annual ammonia budget of fertilised cut grassland – Part 1: Micrometeorological flux measurements and emissions after slurry application

Abstract

Abstract. Two commercial ammonia (NH3) analysers were customised to allow continuous measurements of vertical concentration gradients. The gradients were used to derive ammonia exchange fluxes above a managed grassland site at Oensingen (Switzerland) by application of the aerodynamic gradient method (AGM). The semi-continuous measurements during 1.5 years covered five complete growth-cut cycles and included six applications of liquid cattle slurry. The average accuracy of the flux measurements during conditions of well established turbulence was 20% and the detection limit 10 ng NH3 m−2 s−1, hence sufficient for studying the background exchange of NH3. Quantifying emissions after slurry applications required the application of elaborate interpolations because of difficulties capturing the initial emissions during manure spreading in some parts of the experiments. The emissions were also calculated with a mass balance method (MBM) yielding similar fluxes. NH3 losses after slurry application expressed as percentage of emitted nitrogen versus applied total ammoniacal nitrogen (TAN) varied between 4 and 19%, which is lower than typical values for broadspreading of liquid manure. The comparatively low emission factors appear to be a consequence of the rather thin slurry applied here and soil properties favouring ammonium adsorption.