Nitrous oxide production from granular nitrogen fertilizers applied to a silt loam soil

One field and two laboratory experiments were conducted to determine the relative magnitude and pattern of N 2 O production from several granular N fertilizers including urea, ammonium nitrate, calcium nitrate, ammonium sulfate and, in a laboratory experiment, monoammonium and diammonium phosphates. Several parameters, in particular soil water content, were studied for their roles in N 2 O production with these fertilizers. The field experiment was conducted at the Elora Research Station (20 km north of Guelph) on Conestoga silt loam during July on a site previously cropped to barley. Three methods were employed to assess N 2 O production following N fertilizer treatments in the field experiment, viz., soil cover, soil core and profile distribution. The data with each method revealed that incorporated urea produced the greatest quantity of N 2 O especially in the first few days following application. Shortly after urea application and incorporation (10 cm), N 2 O was detected at a depth of 50 cm indicating gas produced in the tilled layer was transported to lower depths. Data obtained with the intact core method showed that nitrification preceeded denitrification as the source of N 2 O produced during a wetting event as air-filled porosity decreased from 65% to less than 50%, respectively. The laboratory experiments showed that under aerobic conditions N 2 O production was generally greater with urea than the other N fertilizers. The greater production of N 2 O with urea was associated with N 2 O-accumulation. In the second laboratory experiment, saturating the soil following 14 d of aerobic incubation showed enhanced N 2 O production with ammonium phosphate fertilizers. Our findings indicate refinement of methods to predict N 2 O emissions based on N fertilizer source use and moisture can reduce uncertainties in national estimates of N 2 O emissions from agricultural soils. Key words: Nitrous oxide production, nitrogen fertilizers, soil atmosphere profiles, nitrification, denitrification, air-filled porosity