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Green manuring of legume crops can improve soil fertility and sustainability. To evaluate its agronomic and environmental effectiveness, gaseous losses of ammonia (NH3) in the surface layer need to be quantified by direct measurements in the field. However, the application of the eddy-covariance technique to atmospheric NH3 is challenging: its high reactivity, water solubility, and low background concentrations all hinder the response time of closed-path sensors for fast measurements of NH3 concentration. Ammonia emissions following green manuring were measured for 21 days using a flux system equipped with a fast-pulsed quantum-cascade tunable-infrared-laser spectrometer. The noisy cross-covariance function for this configuration indicates flux measurements are close to the limit of detection; the low signal-to-noise ratio further increases the uncertainties, introducing a mirroring effect on the fluxes, which results in the rapid alternation between emission and deposition, within the limit of detection (around 13 and 20 ng m−2 s−1, at the 95 and 99% confidence limits, respectively). An evaluation of the measurement errors is presented, focussing on three technical aspects of the eddy-covariance system: (1) time lag, (2) random error, and (3) limit of detection. The NH3 fluxes measured by the spectrometer are close to its limit of detection, with a random error of the same order as the flux. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3 ) 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. NH 3 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 NH 3 concentration measurements based on Tunable Infrared Laser Differential Absorption Spectrometry (QC-TILDAS). NH 3 volatilisation has been monitored in continuous for both experimental trials, confirming the rapidity of the NH 3 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 NH 3 emission levels were 138.3 and 243.5 μg m −2 s −1 and the total losses of NH 4 -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 NH 3 emissions (such as cloudy with low solar radiation and temperature). [ABSTRACT FROM AUTHOR]