Ammonia Volatilization From Urea and Alternative N Sources in Central Oregon.

Kentucky bluegrass seed fields in central Oregon use surface-applied nitrogen fertilizers.  Fertilizer is generally applied following the conclusion of the irrigation season in mid October and is dependent on natural precipitation for incorporation. Volatile nitrogen loss as ammonia (NH₃) is an economic and environmental concern. The objective of this study was to quantify ammonia volatilization from different nitrogen sources including urea, urea coated with the urease inhibitor (N-(n-butyl) thiophosphoric triamide (NBPT), trade name Agrotain) at a concentration of 1.5 and 3 lbs/ton, and ammonium nitrate applied to the soil surface in the fall in two commercial fields near Madras and Culver in central Oregon. Ammonia volatilization losses were measured with a modified passive flux method, which consisted of a rotating 10 ft tall mast placed at the center of each 100 ft diameter plot. Ammonia volatilization losses were sampled at five heights using glass tubes coated with oxalic acid. Nitrogen was applied at the rate of 150 lbs/ac and monitored over a three-week period.   At both locations, nitrogen loss due to ammonium volatilization was highest with urea (23-25%) followed by Agrotain-coated urea at 1.5 lbs/ton (12-18%) and Agrotain-coated urea at 3 lbs/ton (10-12%). Ammonium nitrate generated the least amount of volatilization (2-4%). Maximum temperatures and the amount of dew/frost appear to be factors affecting ammonia volatilization under these conditions in central Oregon.