Field-scale ammonia emissions from surface spreading of dairy slurry in Po Valley

Po Valley (Northern Italy) is one of the major ammonia (NH₃) emitting regions of Europe, where the slurry spreading causes high NH₃ volatilisation, reducing its agronomic value and becoming a potential cause of environmental concerns. In autumn 2011 a field trial was conducted to estimate the NH₃ losses from the application of dairy slurry at rate of 57 m³ ha^-1 on bare soil. The emissions were estimated from surface application of dairy slurry by using an inverse dispersion modelling technique associated with long term exposure passive samplers and the measure of the atmospheric turbulence. NH₃ emissions levels resulted high within the first 24 hours from the spreading, reaching the 73% of the entire losses, with a maximum value of 163 μg m^-2 s^-1 after 3 hours and 20 minutes, whereas the 50% of the emissions was achieved after 10 hours. The phenomenon stopped after 168 hours with a total NH₃ losses equal to 44% of the total ammoniacal nitrogen (TAN) applied. Results showed and confirmed that surface application involves high NH₃ emissions and then alternative low-emission techniques have to be adopted.