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This article in SSSAJ

  1. Vol. 57 No. 1, p. 93-95
    Received: Nov 11, 1991

    * Corresponding author(s):
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Measuring Nitrogen-15 Content of Gases: Comparison of Direct and ARC-Redistribution Methods

  1. R. J. Buresh  and
  2. E. R. Austin
  1. ICRAF, P.O. Box 30677, Nairobi, Kenya
    IFDC, P.O. Box 2040, Muscle Shoals, AL 35662



When 15N-enriched N2 gas evolves from a soil fertilized with a 15N-labeled source and mixes with atmospheric N2, the mixture will have a nonrandom N isotopic distribution. The 15N enrichment of N2 in air samples can be determined by measuring the ion signals for mass to charge (m/e) 28, 29, and 30 (direct method). An alternative is to randomize the N isotope distribution with a high voltage arc and then determine the 15N enrichment by measuring the ion signals for m/e 28 and 29 (arc method). The 15N enrichments obtained by the direct method and the are method agreed within 1% for (i) 15N-labeled N2 mixed with air and (ii) gases evolved from urea-15N applied to flooded soil. A slight loss of precision in the are method may result from the correction of 15N values for the N blank associated with processing of the samples before isotope ratio analyses. Storage of 15N-enriched air samples in evacuated serological tubes resulted in dilution of their 15N content by the residual air initially present in the tubes; consequently, the 15N values must be corrected for the N content of the residual air.

Research conducted as part of International Fertilizer Development Center (IFDC) and International Rice Research Inst. (IRRI) Co-operative Project, P.O. Box 933, 1099 Manila, Philippines. Joint contribution from IFDC and IRRI.

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