EMISSION-SPECTROMETRY FOR DIRECT MEASUREMENT OF NITROUS-OXIDE AND DINITROGEN FROM SOIL

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 N-15 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-degrees-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 N-15-N2O was reduced to N-15-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 N-15-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 N-15-KNO3. This method can measure both N2O and N2 produced in soil from N-15-enriched fertilizer.