MEASUREMENT OF GASEOUS EMISSIONS FROM DENITRIFICATION OF APPLIED N-15.1. EFFECT OF COVER DURATION

Measurement of gas emissions from denitrification of applied N has bee n restricted because of the lack of a convenient method. Recently a me thod using an electric are to measure N-15 contents of dinitrogen (N-2 ) and nitrous oxide (N2O) in air has been developed. Gas emissions fro m denitrification of applied N-15 were determined using this method fo r gas analysis of the N-15(2) and (N2O)-N-15 captured beneath an air-t ight soil cover. Loss of N-15 was calculated from gas emission measure ments by two methods, accumulation of daily emissions and from the pea k N-15 emission value by assuming linear increase and decrease over th e period of emissions. Losses estimated at low emissions with incomple te soil saturation were similar (1.9-5.6% N-15 applied) for the two me thods. Losses estimated at higher emissions with complete soil saturat ion were higher when calculated using peak emission values (14.8-28.5% ) rather than accumulated daily emissions (9.5-18.7%). Losses estimate d by emissions were compared with N-15 loss estimated by mass balance at the completion of two successive soil saturations. As daily cover d uration was shortened, gas emission estimates of loss more closely app roximated total gaseous N-15 as estimated from unaccounted for N-15 in the N-15 balance. With shortest cover duration (15 min day(-1)) there was close agreement (94% estimated from peak emissions) with N-15 los s estimated by N-15 balance. A strategy for quantitatively estimating N-15 loss by emission measurements is suggested.