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.