The impact of management practices and meteorological conditions on ammonia and nitrous oxide emissions following application of hog slurry to forage grass in Nova Scotia

Nitrogen (N) loss from field-applied slurry through ammonia (NH3) volatilisation has led to the adoption of conservation strategies. While several strategies have been effective, concern is growing that some may simultaneously enhance nitrous oxide (N2O) emissions, thus negating their overall benefits. This study evaluated the impact of slurry application rate, soil water status (dry vs. wet), simulated rainfall (irrigation), slurry dilution and meteorological conditions on NH3 and N2O emissions following application of hog slurry to forage grass. Increasing the slurry application rate increased NH3 losses. Applying slurry to wet soil increased NH3 losses on average by 8%. Simulated rainfall (irrigation) after slurry application reduced NH3 losses by 45%, while diluting slurry decreased NH3 emissions by 41%. Ammonia volatilisation increased with higher air and soil temperatures, net radiation, vapour pressure deficit, and evapotranspiration rates. Due to low soil NO3−-N contents (<5 mg kg−1 soil) caused by slow nitrification activity, all the management strategies and meteorological conditions evaluated had no effect on N2O emissions. Therefore, NH3 losses can be reduced without increasing N2O losses by using proper rates, diluting slurry, applying slurry before forecasted light rainfall (∼6 mm), and most importantly applying slurry during cool days with reduced evaporative demand. Since estimated indirect N2O emissions (i.e., emissions due to volatilised NH3) were higher than direct emissions, more effort should be directed towards reducing NH3 volatilisation after applying slurry to these soils.