Ammonia volatilization after slurry spreading in North Italy: comparison between eddy covariance measurements and inverse dispersion modelling

Ammonia (NH3) volatilization after organic and inorganic fertilizers should be measured by means of non-invasive methodologies like micrometeorological ones in order to avoid alteration of processes involved in the phenomenon. The eddy covariance (EC) technique could be an optimal solution for monitoring NH3, but, nowadays, it is considered a challenge by scientific community due to the difficulties encountered in its actual application. In particular, few data are available in literature and, in general, an underestimation of NH3 fluxes is reported by experimental trials carried out both in laboratory and field. An experimental campaign was carried out in North Italy during and after slurry spreading on bare soil at the end of March 2009. An improvement of the EC system used for the first time during a trial in South Italy in 2008 was employed for measuring the NH3 fluxes. The EC system was equipped with a sonic anemometer (Gill-R2, UK) and a fast-response sensor for NH3, the compact QC-TILDAS-76 SN002-U developed by Aerodyne Research Inc. (ARI, USA). Great care was put in the setup of the system, facing the issues of power supply, thermal stability of the fast response NH3 detector and the warming of its inlet tube to avoid inside water condensation. Moreover, the input data needed for running the inverse dispersion model "FIDES" were collected in order to compare the performance of the EC system with these simulated data. An underestimation by the EC system was recorded with respect to the FIDES simulated data, even if this underestimation was lower than the results obtained by the same EC system during the previous trial. The observed differences between the two approaches are discussed, especially in terms of flux footprint and high frequency loss corrections. These results confirm the efficacy of the above mentioned improvements, even if the question about the applicability on large scale of the EC approach to NH3 monitoring is still open