Ammonia volatilization from farm tanks containing anaerobically digested animal slurry

Ammonia (NH3) volatilization from three full-scale tanks containing anaerobically digested animal slurry from one biogas plant was determined with a meteorological mass balance technique. No surface crust developed on the slurry. This provided an ideal system for analysing loss patterns from slurries without cover and to study the effect of a cover of straw and air-filled clay granules. Ammonia volatilization from uncovered slurry ranged from zero at subzero temperatures to 30 g N m−2 d−1 during summer. The high volatilization rate was attributed to a lack of surface cover, high slurry pH and high TAN (NH3 + NH4+) concentration. Ammonia volatilization from the covered slurry was insignificant. From the uncovered slurry the annual loss of NH3 was 3.3 kg N m−2 There was a significant effect of incident global radiation (ICR), air temperature at 20 cm (T_20) and rain on NH3 volatilization from the uncovered slurry. The straw covered slurry was significantly affected by T_20.