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.