Measurement of gaseous emissions from denitrification of applied N-15 .I. Effect of cover duration

Abstract

Measurement of gas emissions from denitrification of applied N has been restricted because of the lack of a convenient method. Recently a method using an electric are to measure 15N contents of dinitrogen (N2) and nitrous oxide (N2;O) in air has been developed. Gas emissions from denitrification of applied 15N were determined using this method for gas analysis of the 15N2 and 15N2O captured beneath an air-tight soil cover. Loss of 15N was calculated from gas emission measurements by two methods, accumulation of daily emissions and from the peak 15N emission value by assuming linear increase and decrease over the period of emissions. Losses estimated at low emissions with incomplete soil saturation were similar (1.9 - 5.6% 15N applied) for the two methods. Losses estimated at higher emissions with complete soil saturation were higher when calculated using peak emission values (14.8 - 28.5%) rather than accumulated daily emissions (9.5 - 18.7%). Losses estimated by emissions were compared with 15N loss estimated by mass balance at the completion of two successive soil saturations. As daily cover duration was shortened, gas emission estimates of loss more closely approximated total gaseous 15N as estimated from unaccounted for 15N in the15N balance. With shortest cover duration (15 min day-1) there was close agreement (94% estimated from peak emissions) with 15N loss estimated by 15N balance. A strategy for quantitatively estimating 15N loss by emission measurements is suggested.