Nitrous oxide flux measurements from an intensively managed irrigated pasture using micrometeorological techniques

Nitrous oxide emissions from flood-irrigated pastures grazed for dairy production were measured over 2 years using micrometeorological techniques. Turbulent atmospheric transfer coefficients derived from fluxes of sensible heat and momentum were used to estimate the N2O fluxes from concentrations measured at two heights. Careful data selection excluded data for periods of very low wind-speed and strong stability when transfer coefficients were unreliable. The measurements demonstrated the dynamic nature of N2O emissions following grazing, fertiliser application and irrigation. Daily-averaged emissions ranged from <4 to close to 170 g N2O-N ha−1 day−1. High emissions due to denitrification occurred when soil temperatures were >15 °C, nitrogen was available following grazing or fertiliser application and the water filled pore space of the soil was in the range 65–95%. N2O emission factors of 0.23 ± 0.06% for grazing were similar to those for fertiliser application plus grazing (0.32 ± 0.12%).