Ammonia emissions from liquid manure storages are affected by anaerobic digestion and solid-liquid separation

The effects of manure management practices on ammonia (NH3) emissions were evaluated using a micrometeorological technique at four contrasting dairy storage facilities: untreated raw manure slurry (RM), solid-liquid separation with storage of separated liquids (SL), anaerobic digestion of manure and off-farm materials (AD), and anaerobic digestion with solid-liquid separation and storage of the liquid fraction (ADL). Annual average NH3 emissions per surface area were lowest for RM (2.7 g m(-2) d(-1)), followed by SL (4.5 g m(-2) d(-1)), AD (10.0 g m(-2) d(-1)), and ADL (15.5 g m(-2) d(-1)). Lower NH3 emissions from the RM storage were partly due to the 30 cm thick surface crust which formed on the storage surface in summer (wood shavings was used as bedding). Greater surface crusting at the AD storage compared to the ADL storage was also likely the reason for higher emissions at the ADL storage. Relationships between NH3 emissions, temperature, and wind-speed were observed at all sites but were strongest at sites with minimal crusting (SL, ADL) and weak at the RM storage with a crust cover. Total NH3 emissions from each storage facility (kg y(-1)) did not simply track the differences in fluxes; rather, facilities with greater storage (RM, AD, ADL) had higher emissions than the facility with less storage (SL) due to removal of solids and more frequent field application. Overall, bedding material, manure processing, and storage management all have important effects on NH3 emissions from manure storage.