Evaluation of nitrogen-15 tracer techniques for direct measurement of denitrification in soil: III. Laboratory studies

Laboratory studies were conducted to evaluate the assumption of isotopic uniformity that underlies mass spectrometric determination of dinitrogen (N₂) and nitrous oxide (N₂O) evolved during denitrification in soil treated with ¹⁵N-labeled fertilizer. In these studies, a gas chromatograph (GC) and mass spectrometer (MS) were used to analyze replicate atmospheric samples containing N₂O generated through oxidation of ¹⁵N-labeled NH₂OH, evolved from ¹⁵N-treated soil slurries incubated at constant moisture content (1 kg H₂Okg^-1), or evolved from N-treated soil subjected to wetting and drying cycles. Both instruments gave almost identical values in analysis of N₂O derived from a single pool of ¹⁵N-labeled NH₂OH or from two pools having similar, but not necessarily the same, enrichments. The MS gave lower values for N₂O derived from two pools differing markedly in their enrichment of ¹⁵N.