Effect of Ammonium Sulfate On Ammonia Nitrogen Loss in Irrigated Pacific Northwest.

In the Columbia River Gorge, Pacific Northwest, downwind reactions of ammonia (NH₃) emitted from nearby nitrogen (N) fertilizer use in agriculture form secondary aerosol particles, or light-scattering haze. Nitrogen deposition in the gorge has also caused a shift to more nitrophillic lichen species. Use of urea fertilizers in this semi-arid, Mediterranean climate has resulted in considerable N loss through NH₃ volatilization. NH₃-N loss from urea might be significantly reduced if ammonium sulfate (AMS) is added; past studies have indicated that NH₃-N loss from ammonium sulfate (AMS) application is much lower than loss from urea. A 3 week field trial in October 2009 compared treatments of AMS and urea treated with the urease inhibitor, Agrotain® (n-(n-butyl) thiophosphoric triamide)), applied at a rate of  114 kg N/ha, for efficacy to reduce NH₃ volatilization compared to urea alone. Atmospheric NH₃ flux from treatments was estimated using modified passive flux method samplers and calculations. Average, cumulative NH₃-N loss from Agrotain® and AMS after 3 weeks was 4.8 and 6.8 kg N/ha, amounting to a 72- and 60% reduction of NH₃-N loss, respectively, compared to 17 kg N/ha lost from urea. There was no significant difference between NH₃-N loss from AMS and Agrotain® treatments (LSD, p<0.05); therefore, AMS is a viable alternative to limit NH₃ volatilization versus urea when conditions do not suit the use of Agrotain®. A similar field trial in August 2013 will compare NH₃-N loss rates between treatments of urea, urea treated with Agrotain®, urea with AMS applied separately, ammonium sulfate alone, and a fused, composite, granule of urea + AMS. This research will continue to analyze cultural practices and products that improve N use efficiency.