Measuring Simultaneous Fluxes from Soil of N2O and N2 in the Field Using the 15N-Gas “Nonequilibrium” Technique

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Abstract
Our purpose was to measure simultaneous fluxes from soil of both N2O and N2 from the same plot in the field using the 15N-gas "nonequilibrium" technique (i.e., the "Hauck" technique) as used previously for N2. We accommodated analysis of N2O by modifying the head amplifier of our mass spectrometer. Our system accurately measured the 15N enrichments of labeled soil slurries for both N2 and N2O. In the field, we measured flux of N2 and N2O during soil denitrification from a 15N-labeled plot of winter wheat. Nine chamber incubations were conducted over 4 days. N2 flux ranged from below detection limit (<0.022 g x m(-2) x d(-1)) to 0.055 g x m(-2) x d(-1). N2O flux ranged from 0.0002 to 0.0027 g N2O-N x m(-2) x d(-1), with a detection limit of 1.0 x 10(-6) g N2O-N x m(-2) x d(-1). For N2O flux, the 15N-gas technique and gas chromatography technique agreed well (r = 0.98). The 15N enrichment of the soil mineral pool undergoing denitrification, measured nondestructively using the N2O data, dropped from about 0.82 to 0.72 atom fraction 15N over 4 days. Applying the 15N-gas nonequilibrium technique to N2O complements its use for 15N-N2 analysis when studying the relative production of N2O and N2 during denitrification.