Measuring simultaneous fluxes from soil of N2O and N2 in the field using the 15N-Gas "nonequilihrium" technique

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