Does split-nitrogen application reduce nitrous oxide emissions from irrigated cotton compared with all nitrogen applied pre-season?

Abstract

Key findings •• Nitrous oxide (N2O) emissions at the Gunnedah site were approximately three times higher than at the Emerald site, probably because of the heavier clay soil at Gunnedah. •• High and highly variable N2O emissions occurred at both sites during the week following the first irrigation event after the pre-planting nitrogen (N) application. There was no significant effect from the amount of N applied at pre-planting on these first emissions, nor overall at Gunnedah. At Emerald, overall N2O losses were greater from the split N treatment. •• N2O emissions were low–negligible following the subsequent 4–5 irrigation events, except where N was water-run, which caused small and temporary increases in N2O. •• The greatest N2O emission came from the soil above the pre-plant N fertiliser bands. More was emitted from the non-irrigated side of the plant bed, even when both sides of the bed had been fertilised (Emerald). •• Cotton lint yield was not affected by N timing treatment, however, plant biomass was smaller and more N-concentrated from the split N treatment at Gunnedah. •• The 2015–16 weather conditions did not favour either N-timing treatment agronomically or environmentally, but different rainfall patterns in other years may be more influential.