| Summary: | Pastures require year-round access to water and in some locations rely on irrigation during dry periods. Currently, there is a dearth of knowledge about the potential for using irrigation to mitigate N<sub>2</sub>O emissions. This study aimed to mitigate N<sub>2</sub>O losses from intensely managed pastures by adjusting irrigation frequency using soil gas diffusivity (<i>D<sub>p</sub>/D<sub>o</sub></i>) thresholds. Two irrigation regimes were compared; a standard irrigation treatment based on farmer practice (15 mm applied every 3 days) versus an optimised irrigation treatment where irrigation was applied when soil <i>D<sub>p</sub>/D<sub>o</sub></i> was ≈0.033 (equivalent to 50% of plant available water). Cow urine was applied at a rate of 700 kg N ha<sup>−1</sup> to simulate a ruminant urine deposition event. In addition to N<sub>2</sub>O fluxes, soil moisture content was monitored hourly, <i>D<sub>p</sub>/D<sub>o</sub></i> was modelled, and pasture dry matter production was measured. Standard irrigation practices resulted in higher (<i>p</i> = 0.09) cumulative N<sub>2</sub>O emissions than the optimised irrigation treatment. Pasture growth rates under treatments did not differ. Denitrification during re-wetting events (irrigation and rain) contributed to soil N<sub>2</sub>O emissions. These results warrant further modelling of irrigation management as a mitigation option for N<sub>2</sub>O emissions from pasture soils, based on <i>D<sub>p</sub>/D<sub>o</sub></i> thresholds, rainfall, plant water demands and evapotranspiration.
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