Evaluation of 15N Methods for the measurement of Denitrification in Soils

Abstract The precision of the 15N-emission and that of the 15N-balance methods was evaluated and both methods were compared in a denitrification experiment. 15N-analysis was performed with an isotope ratio mass spectrometer which was coupled to an elemental analyzer. The measuring sensitivity in soil and gas analysis was tested by analyzing 15N-standards. The detection limit for gas samples with two different procedures of 15N-gas analysis was δ15N = (4.5 ± 1.0)‰ and (0.5 ± 0.05)‰, respectively. The error in measurement was 19% and 12% respectively. 15N-analysis of a 15N-labelled soil (4.15 ppm 15N) resulted in a CV of 1.32%. The measurements had to be calibrated with soil standards because the 15N-values showed a continuous downward fluctuation in a range of 10–20% within several days, when only acetanilid was used for calibration. Mean 15N-losses which were determined with both methods during the denitrification experiment were in good agreement. The precision of the 15N-emission method was adequate in ...