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Wiley, Journal of Environmental Quality, 5(42), p. 1327-1340, 2013

DOI: 10.2134/jeq2013.02.0067

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Tracking Short-Term Effects of Nitrogen-15 Addition on Nitrous Oxide Fluxes Using Fourier-Transform Infrared Spectroscopy

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Synthetic fertilizer N additions to soils have significantly increased atmospheric N2O concentrations, and advanced methods are needed to track the amount of applied N that is transformed to N2O in the field. We have developed a method for continuous measurement of N2O isotopologues (NNO, NNO, NNO, and NNO) following 0.4 and 0.8 g N m of N-labeled substrate as KNO or urea [CO(NH)] using Fourier-transform infrared (FTIR) spectroscopy. We evaluated this method using two 4-wk experimental trials on a coastal floodplain site near Nowra, New South Wales, Australia, which is managed for silage production. We deployed an automated five-chamber system connected to a portable FTIR spectrometer with multipass cell to measure N2O isotopologue fluxes. Emissions of all isotopologues were evident immediately following N addition. All isotopologues responded positively to rainfall events, but only for 7 to 10 d following N addition. Cumulative N-NO fluxes (sum of the three N isotopologues) per chamber for the 14 d following N addition ranged from 1.5 to 10.3 mg N m. Approximately 1% (range 0.7-1.9%) of the total amount of N applied was emitted as N2O. Repeatability (1σ) for all isotopologue measurements was better than 0.5 nmol mol for 1-min average concentration measurements, and minimum detectable fluxes for each isotopologue were <0.1 ng N m s. The results indicate that the portable FTIR spectroscopic technique can effectively trace transfer of N to the atmosphere as NO after N addition, allowing powerful quantification of N2O emissions under field conditions.