MEASUREMENT OF FIELD-SCALE N2O EMISSION FLUXES FROM A WHEAT CROP USING MICROMETEOROLOGICAL TECHNIQUES

Measurements of N2O emission fluxes from a 3 ha field of winter wheat were measured using eddy covariance and relaxed eddy accumulation cont inuously over 10 days during April 1994. The measurements averaged flu xes over approximately 10(5) m(2) of the field, which was fertilised w ith NH4NO3 at a rate of 43 kg N ha(-1) at the beginning of the measure ments. The emission fluxes became detectable after the first heavy rai nfall, which occured 4 days after fertiliser application. Emissions of N2O increased rapidly during the day following thr: rain to a maximum of 280 ng N m(-2)s(-1) and declined over the following week. During t he period of significant emission fluxes, a clear diurnal cycle in N2O emission was observed, with the daytime maximum coinciding with the s oil temperature maximum at 12 cm depth. The temperature dependence of the N2O emission was equivalent to an activation energy for N2O produc tion of 108 kJ mol(-1). The N2O fluxes measured using relaxed eddy acc umulation, averaged over 30 to 270 min, were in agreement with those o f the eddy covariance system within 60%. The total emission of N2O ove r the period of continuous measurement(10 days) was equivalent to abou t 10 kg N2O-N, or 0.77% of the N fertiliser applied.