Does Fall Anhydrous Ammonia Lead to Greater Nitrous Oxide Emissions Than Spring Addition?

Under the ‘Four R Stewardship Program' and the ‘Nitrous Oxide Emission Reduction Program (NERP)', the fertilizer industry and farm extension agents promote spring rather than fall anhydrous ammonia application to reduce nitrous oxide emissions on the Canadian Prairies. This study compared late fall and spring application timings of anhydrous ammonia on nitrous oxide emissions. The study was conducted at the Trace Gas Manitoba (TGAS-MAN) study site located in the Red River Valley, Manitoba on a cropped clay soil. Emissions were determined using a tunable diode laser and the micrometeorological, flux-gradient technique, to capture the expected short duration of emissions following applications and emissions occurring as soil thaws in this northern climate. Preliminary observations show late fall application of anhydrous ammonia to result in negligible emissions of nitrous oxide but result in emissions as soil thaws the following year. In contrast, spring application is followed shortly by emission of nitrous oxide for 1-2 weeks. The flux-gradient technique was successful in capturing the ephemeral nature of the emission events impossible with standard chamber methods. Cumulative emission of nitrous oxide for fall and spring anhydrous ammonia treatments will be presented and discussed in regard to recommendation of application timing to reduce emissions.