Evaluation of Nitrogen-15 Tracer Techniques for Direct Measurement of Denitrification in Soil: III. Laboratory Studies
1988
Mulvaney, R. L.
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 H₂O kg⁻¹), or evolved from ¹⁵N-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. The values measured by GC and MS differed significantly (0.05 level) for about 50% of the soil atmospheric samples analyzed; however, the differences usually did not exceed 10% and probably resulted from analytical error rather than lack of isotopic uniformity in the NO⁻₃ denitrified, because in about half of these cases, the greater value was obtained by MS. This study was a part of Project ILLU-15-0392, Illinois Agric. Exp. Stn. Supported in part by the Tennessee Valley Authority.
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