Determination of 30N2 and Application to Measurement of N2 Evolution During Denitrification1
- R. S. Siegel,
- R. D. Hauck and
- L. T. Kurtz2
A method for the precise determination of the 30N2/(28N2 + 29N2) ratio with a dual-inlet ratio mass spectrometer is proposed. Precise measurements of this ratio (SE = 2.4 × 10-7) performed on atmospheric samples taken from enclosed chambers above soils fertilized with highly enriched 15N-labeled KNO3 (63.6 atom % 15N) allowed direct determination of rates of N2 efflux in the field as low as 2.5 g N2 ha-1 day-1 during denitrification. Rates as high as 250 g ha-1 day-1 were also observed. Measurement of the 29N2/28N2 ratio in conjunction with the 30N2/(28N2 + 29N2) ratio in atmospheric samples containing evolved N2 gas allowed calculation of the average 15N enrichment of the NO-3 pool undergoing denitrification in the soil without destructive sampling. Isotopic enrichment of the NO-3 pool in one plot was reduced by one-third after 28 days. Laboratory studies verified the use of 29N2/28N2 and 30N2/(28N2 + 29N2) ratios for the calculation of the 15N content of the NO-3 undergoing denitrification. The laboratory studies showed little effect of mole fraction 15N in isotopically labeled NO-3 on the rate of N2 efflux from flooded soils, indicating microbial activity was not influenced by high concentrations of 15N.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © . .