Direct Measurement of Dinitrogen Evolution from Soil Using Nitrogen‐15 Emission Spectrometry

Abstract

When a 15N‐enriched N source is added to the soil, denitrification results in a nonrandom distribution of N2 isotopes. As a result, it has been necessary to apply highly enriched 15N‐fertilizers to allow mass spectrometry (MS) determinations of 28N2, 29N2, and 30N2 to quantify the N2 evolution. An alternative method, based on the determination of N2 evolution by measurement of the 28N2/29N2 ratio with emission spectrometry (ES), is proposed. An apparatus consisting of a cuvette and a sampling system was developed. The sampling system was evacuated to <10−1 Pa before gas from the cuvette system was fed into a reservoir (10 mL), through a liquid N2 trap and into five discharge tubes for ES. The final pressure in the tubes was 4 to 5 × 102 Pa before they were sealed off, and the 28N2/29N2 ratios in the gases were determined with ES. It was verified that random distribution of 28N2, 29N2, and 30N2 was obtained in different N2‐gas mixtures made from natural atmosphere and 98 atom % 15N‐N2 by the high frequency discharge of the ES. The system was used to measure fertilizer N2 loss when 15N‐enriched KNO3 was applied at a depth of 2.5 cm in flooded soil. After 60 d, 18% of the applied KNO3 was lost as N2.

Comparison of methods to determine triple oxygen isotope composition of N2O

“…[13] The latter has also been used for measuring N 2 from denitrification tracer experiments where 15 N is distributed non-statistically among the N 2 molecules. [14][15][16] Here, we present a comparison of the gold wire oven [12] and the MIP [13] methods. In addition, the use of a corundum tube in the MIP reactor was tested to see if it produced better results than the quartz tube used in the original method.…”

“…Published methods for the transformation of N 2 O into N 2 and O 2 use either a heated gold catalyst or a microwave‐induced plasma (MIP) . The latter has also been used for measuring N 2 from denitrification tracer experiments where 15 N is distributed non‐statistically among the N 2 molecules …”

Isotopic Techniques to Measure N2O, N2 and Their Sources

“…Double collector IRMS required two measurements with the IRMS so that either 29 N 2 or 30 N 2 is positioned on the first collector (Siegel et al 1982). Emission spectroscopy has also been used in the past to detect 28 N 2 , 29 N 2 and 30 N 2 (Kjeldby et al 1987), but its relatively low precision enabled only detection of large N 2 fluxes. While dual inlet IRMS had been used with manual measurement of samples in glass containers that were sealed (Well et al 1993) or isolated by stopcocks (Siegel et al 1982), continuous flow IRMS enables automated injection of samples from septum capped vials since the 1990s (Stevens et al 1993 (Brand et al 2009, Siegel et al 1982 due to the omnipresence of oxygen traces.…”