The annual ammonia budget of fertilised cut grassland — Part 1:Micrometeorological flux measurements and emissions after slurryapplication

摘要

Two commercial ammonia (NH3) analysers werecustomised to allow continuous measurements of verticalconcentration gradients. The gradients were used to deriveammonia exchange fluxes above a managed grassland site atOensingen (Switzerland) by application of the aerodynamicgradient method. The measurements from July 2006 toOctober 2007 covered five complete growth-cut cycles andincluded six applications of liquid cattle slurry. The averageaccuracy of the flux measurements during unstable andnear-neutral conditions was 20% and the detection limitwas 10 ngNH3 M-2 s-1. Hence the flux measurements areconsidered sufficiently accurate for studying typical NH3deposition rates over growing vegetation. Quantifyingthe overall emissions after slurry applications required theapplication of elaborate interpolations because of difficultiescapturing the initial emissions during broadspreading ofliquid manure. The emissions were also calculated witha mass balance method yielding similar fluxes. NH3 lossesafter slurry application expressed as percentage of emittednitrogen versus applied total ammoniacal nitrogen (TAN)varied between 4 and 19%, which is roughly a factor of threelower than the values for broadspreading of liquid manurein emission inventories. The comparatively low emissionfactors appear to be a consequence of the low dry mattercontent of the applied slurry and soil properties favouringammonium adsorption.