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

Abstract

Abstract. Two commercial ammonia (NH 3 ) 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. The measurements from July 2006 to October 2007 covered five complete growth-cut cycles and included six applications of liquid cattle slurry. The average accuracy of the flux measurements during unstable and near-neutral conditions was 20% and the detection limit was 10 ngNH 3 m −2 s −1 . Hence the flux measurements are considered sufficiently accurate for studying typical NH 3 deposition rates over growing vegetation. Quantifying the overall emissions after slurry applications required the application of elaborate interpolations because of difficulties capturing the initial emissions during broadspreading of liquid manure. The emissions were also calculated with a mass balance method yielding similar fluxes. NH 3 losses after slurry application expressed as percentage of emitted nitrogen versus applied total ammoniacal nitrogen (TAN) varied between 4 and 19%, which is roughly a factor of three lower than the values for broadspreading of liquid manure in emission inventories. The comparatively low emission factors appear to be a consequence of the low dry matter content of the applied slurry and soil properties favouring ammonium adsorption.

Determination of field scale ammonia emissions for common slurry spreading practice with two independent methods

“…Two adjacent fields cultivated as cropland (wheat) and intensively managed grassland (grass-clover mixture) were fertilised with liquid cattle slurry. The grassland is one of the level 3 sites of the NitroEurope project (www.nitroeurope.eu) and NH 3 concentrations as well as exchange patterns had been investigated here previously (Norman et al, 2009;Spirig et al, 2010;Wolff et al, 2010;Flechard et al, 2010Flechard et al, , 2011. The climate is temperate continental with mean annual temperature and rainfall of 9.5 • C and 1200 mm, respectively.…”

“…It has been tested in a tracer experiment (Tuzson et al, 2010) and has performed well in a state-of-the-art footprint intercomparison (Kljun et al, 2003). The footprint correction for flux divergence is valid, given (i) negligibly small flux interference of chemical conversion of NH 3 to particulate NH + 4 between the surface and measurement level with the high emissions following fertilisation , and (ii) the small impact of storage of NH 3 in the corresponding air column on the measured flux (<1 %, determined following Spirig et al, 2010). Specifically, with the footprint analysis the relative contributions of each slurry track and outer regions to the measured EC fluxes were quantified.…”

“…It comprises values between 4 % to almost 100 % (e.g. Pain et al, 1989;Braschkat et al, 1997;Génermont et al, 1998;Menzi et al, 1998;Huijsmans et al, 2001;Søgaard et al, 2002;Huijsmans et al, 2003;Misselbrook et al, 2002Misselbrook et al, , 2005aSanz et al, 2010;Spirig et al, 2010;Uusi-Kämppä and Mattila, 2010). The strong stickiness of the polar NH 3 molecule complicates measurements of ambient NH 3 concentrations (Parrish and Fehsenfeld, 2000;von Bobrutzki et al, 2010) and consequently fluxes.…”

“…Varying instrumental performance Sutton et al, 2009) and limited signal range of sensors introduce large uncertainties into NH 3 emission quantifications. The possibility for accurate field scale assessments under common agricultural practice is important for the validation of emission levels (Sommer et al, 2003;Spirig et al, 2010). Agricultural practice means that the slurry spreading is not performed instantaneously, but as a sequence of dispersals over a period of typically one to several hours.…”

TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen

“…Furthermore, NH 3 was measured additionally by a wet chemical AiRRmonia instrument (Erisman et al, 2001;Spirig et al, 2010; (Table 1). Time series of NH 3 measured by the AiRRmonia system, gap-filled HNO 3 , HONO, NH + 4 , NO − 3 data of the GRAEGOR, and NO, NO 2 data of the TEI are shown in Fig.…”