Ammonia and nitrous oxide emissions following land application of high and low nitrogen pig manures to winter wheat at three growth stages

Nitrous oxide (N₂O) and ammonia (NH₃) emissions from surface applied high (HN) and low (LN) nitrogen pig manures were measured under field conditions. Manures were band-spread to a winter wheat crop at three growth stages—mid-tillering, stem elongation and flag leaf emergence. The N₂O flux rates were measured using the static chamber technique while NH₃ volatilisation was assessed using a micrometeorological mass balance technique with passive flux samplers. The N₂O emissions were episodic in nature with flux rates observed ranging from 2.8 to 31.5 g N₂O–N ha^?1 day^?1 (P < 0.001). Higher N₂O emissions generally occurred after rainfall events. Highest N₂O losses were observed from the HN treatment with LN manure use decreasing emissions by 18% (P < 0.03). The NH₃ volatilisation rates were highest within 1 h of manure application with 95% of emissions occurring within 24 h (P < 0.001). Cumulative N loss was highest at mid-tillering as low crop canopy cover and increased wind-speeds enhanced NH₃ loss (P < 0.001). Highest emissions were measured from the HN manure (P < 0.03). Total ammoniacal N loss ranged from 6 to 11%. Crop N uptake and grain yield were unaffected by application timing or manure type. Therefore, the use of LN manures decreased gaseous emissions of N₂O and NH₃ without any adverse effects on crop performance.