Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements

Abstract

Abstract.Quantification of ammonia (NH 3 ) landatmosphere exchange is required for atmospheric modelling and assessment of nitrogen deposition, yet flux measurement methods remain highly uncertain. To address this issue, a major inter-comparison of ammonia fluxes over intensively managed grassland was conducted during the GRAMINAE Integrated Experiment held in Braunschweig, Germany. In order to provide a robust dataset of ammonia exchange with the vegetation, four independent continuous flux gradient systems were operated. Three independently operated continuous wet denuders systems (AMANDA) were compared with a Wet Effluent Diffusion Denuder (mini-WEDD) system. Measurements were made at two distances from an adjacent livestock farm, allowing effects of advection to be quantified in a real landscape setting. Data treatment included filtering for instrument failure, disturbed wind sectors and unsuitable micrometeorological conditions, with corrections made for storage and advection errors.The inter-comparison demonstrated good agreement in measured ammonia concentrations and fluxes (relative standard error <20%) for some periods, although the performance of the ammonia analyzers were variable, with muchCorrespondence to: C. Milford (cmilford@inm.es) poorer agreement on particular days. However, by using four systems, the inter-comparison was able to provide a robust mean estimate of continuous ammonia fluxes through the experiment. The observed fluxes were: a) small bi-directional fluxes prior to cutting (−64 to 42 ng NH 3 m −2 s −1 ), b) larger diurnally-varying emissions following cutting (−49 to 703 ng NH 3 m −2 s −1 ) and c) much larger emissions following fertilizer application (0 to 3820 ng NH 3 m −2 s −1 ). The results are a salutary reminder of the uncertainty in unreplicated ammonia flux measurements, while the replication of the present study provides a uniquely robust dataset for the evaluation of ammonia exchange processes. It is clear that consistently reliable determination of ammonia concentrations remains the major measurement challenge.

Seasonal variation in nitrogen pools and &lt;sup&gt;15&lt;/sup&gt;N/&lt;sup&gt;13&lt;/sup&gt;C natural abundances in different tissues of grassland plants

“…Nitrogen fertilization also gives rise to NH 3 emission Larsson et al, 1998;Ross and Jarvis, 2001;Sutton et al, 2001;David et al, 2009;Mattsson et al, 2009;Milford et al, 2009;Flechard et al, 2010;Hojito et al, 2010). The magnitude of NH 3 emission following fertilization may be much larger than that after cutting .…”

“…Episodes of NH 3 emission from grasslands have frequently been observed in response to cutting (Sutton et al, 1998(Sutton et al, , 2001David et al, 2009;Mattsson et al, 2009;Milford et al, 2009). Nitrogen fertilization also gives rise to NH 3 emission Larsson et al, 1998;Ross and Jarvis, 2001;Sutton et al, 2001;David et al, 2009;Mattsson et al, 2009;Milford et al, 2009;Flechard et al, 2010;Hojito et al, 2010).…”

“…In intensively managed grasslands, fertilizers represent the major source of N input, and repeated cuttings and/or continuous grazing are the major normal management practices. Large NH 3 emissions may be recorded after N fertilization Milford et al, 2009;Hojito et al, 2010), slurry application (Flechard et al, 2010) and also following cutting of the grass canopy . Grazing events may also have effects on grassland NH 3 fluxes (Loubet et al, 2002) and N status (van Hove et al, 2002;Li et al, 2010) and may promote availability of N in N-limited grasslands by increasing N cycling and NO − 3 assimilation (Frank and Evans, 1997).…”

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

“…Analytical difficulties in NH 3 measurements may originate from gas-phase calibration uncertainties (von Bobrutzki et al, 2010), drifting instrumental stability , selective sampling and analysis of gas and aerosol phase and NH 3 sorption in filters, tubes and devices (Parrish and Fehsenfeld, 2000). Flux measurements with the aerodynamic gradient method using AMANDA instruments are associated with uncertainties of 20 % to 76 % (Sutton et al, 2000;Milford et al, 2009). After fertilisation, relaxed eddy accumulation approaches have underestimated NH 3 fluxes compared to the AMANDA gradient systems by 20 % to 70 % while EC measurements based on laser absorption spectrometry have exhibited biases in the order of −50 % when related to the AMANDA fluxes (Whitehead et al, 2008).…”

Investigating the stomatal, cuticular and soil ammonia fluxes over a growing tritical crop under high acidic loads

“…There are a few studies reporting ammonia flux measurements over grassland (Flechard et al, 2010;Milford et al, 2009;Sutton et al, 2009aSutton et al, , 2009bWichink Kruit et al, 2007), and semi-natural ecosystems (Flechard and Fowler, 1998a;Flechard and Fowler, 1998b;. However, even if the previous ecosystems have not been extensively studied, there are even less reference fluxes above croplands (Sutton et al, 1995), and most of them focus on NH 3 volatilisation following fertiliser application or slurry spreading (Genermont et al, 1998;Loubet et al, 2010).…”