Ammonia emissions from rough cattle slurry and from derived solid and liquid fractions applied to alfalfa pasture

A field trial was conducted to assess the emission of ammonia from rough cattle slurry and solid and liquid fractions (generated from its mechanical separation) applied to alfalfa pasture. Three materials (rough slurry, liquid fraction and solid fraction) were applied on alfalfa over two seasons (summer and autumn), with two application rates (40 and 70 kg N/ha) and with two air velocities (0–0.6 m/s) at the soil surface. Ammonia losses were measured either by a set of wind tunnels (adjusting the air velocity at 0.6 m/s) or by a funnel system, allowing measurements to be recorded at an air speed close to 0 m/s. Each trial lasted 5 days with daily sampling of the gaseous emissions. Trial results showed that the rough slurry substrate had the highest level of ammonia emissions, followed by the liquid and solid fractions. Up to 35% of the applied total Kjeldahl nitrogen was lost as ammonia from the rough slurry in 5 days in summer conditions and with an air velocity of 0.6 m/s. No effect due to the application rate was observed, however, a significant effect of the temperature and air velocity on ammonia emissions was measured. Ammonia emissions after the spreading of the rough slurry were up to 26% higher when compared with those generated after application of the two fractions (solid + liquid).