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Emission Spectrometry for Direct Measurement of Nitrous Oxide and Dinitrogen from Soil

The Phytotron, Univ. of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, Norway

*Corresponding author.

ABSTRACT

Measurement of N₂O and N₂ produced by denitrification is of current interest, from an environmental point of view and for the quantification of N losses. Our method for direct measurement of N₂ evolution from soil by ¹⁵N emission spectrometry (ES) has been modified to measure both N₂O and N₂. Two different methods for reduction of N₂O to N₂ before measurement by ES were tested: (i) by catalyst (Al₂O₃ + 0.5% Pd) and high temperature (700 °C) in the gas sampling system (method I) and (ii) by high-frequency discharge in the ES discharge tubes (Method II). By catalyst, 93% of ¹⁵N-N₂O was reduced to ¹⁵N-N₂, while 98% was reduced by high-frequency discharge in the ES discharge tubes. The application of the two methods was tested by measuring the N₂O and N₂ losses in closed cuvette systems after ¹⁵N-enriched KNO₃ was added to moist (85% of field capacity) and flooded soil. The nitrification inhibitor dicyandiamide was mixed into the moist soil to prevent loss of N₂O as a result of nitrification. The same results were obtained when the N₂O loss from moist soil was determined by using Method I, Method II, or gas chromatography (GC). The ratio of N₂O/N₂ was 2.9 for moist soil and 0.2 for flooded soil 2 wk after application of ¹⁵N-KNO₃. This method can measure both N₂O and N₂ produced in soil from ¹⁵N-enriched fertilizer.

Received for publication August 27, 1991.