Dynamics of ammonia volatilisation measured by eddy covariance during slurry spreading in north Italy

Ammonia (NH3) emissions have been quantified during slurry spreading in two experimental trials in two intensively managed agricultural fields in northern Italy, during spring 2009 and 2011. NH3 fluxes have been measured by Eddy covariance (EC) method from the slurry application to the soil incorporation until the end of the emission phenomenon. The EC system was equipped with a fast sensor for NH3 concentration measurements based on Tunable Infrared Laser Differential Absorption Spectrometry (QC-TILDAS). NH3 volatilisation has been monitored in continuous for both experimental trials, confirming the rapidity of the NH3 losses when slurry is spread to the field. Within 24 h from the application the volatilisation suddenly decreases, stopping after soil incorporation occurred 24 and 30 h from the spreading for the two experimental trials. The maximum NH3 emission levels were 138.3 and 243.5 μg m−2 s−1 and the total losses of NH4-N were 19.4% and 28.5%, determined 7 days after the spreading for the first and the second trial, respectively. EC measurements have been compared to the emissions estimated by a backward Lagrangian stochastic model, resulting consistent for dynamic and quantitative emitted. To explain the differences between the losses in the two experiments, the relationship between emission and meteorological conditions has been investigated. In particular, rain during the 2009 trial caused a significant reduction in emissions, whereas high air temperatures enhanced the emission phenomenon in the 2011 trial. The results shown that for improving nitrogen efficiency, slurry incorporation has to be performed in times closer from spreading than 24 h, under weather conditions which limit NH3 emissions (such as cloudy with low solar radiation and temperature).