Assessing the Impact of Stabilized Urea Fertilizers on Ammonia Volatilization Under Controlled Environment and Soil Conditions.

Ammonia volatilization is one of the major loss pathways when urea fertilizers are applied to the soil surface. Under management conditions where no alternatives for surface application are available, strategies such as using stabilized urea fertilizers (i.e. fertilizers containing either nitrification or urease inhibitors, or both) have been emphasized to reduce ammonia volatilization. The soil pH, moisture content, and temperature are important factors governing ammonia emissions, and the magnitude by which stabilized urea fertilizers reduce these emissions might be dependent on these conditions. Under soil conditions where low ammonia emissions occur, using stabilized fertilizers might be less effective, compared to conditions highly favoring ammonia conditions. The impact of these soil factors on ammonia emissions from stabilized fertilizers is not known, though the ability to predict losses under certain soil conditions could positively impact decision-making in fertilizer management. We studied the ammonia emissions from four different stabilized fertilizers as well as urea under lab conditions in which soil pH, moisture content and temperature were manipulated. The system for measuring ammonia volatilization consisted of three temperature controlled cabinets in which an air flow was guided through soil chambers and emissions were monitored. The inhibitors contained in the stabilized fertilizers were the urease inhibitor N-Butyl thiophosphoric triamide (NBPT, contained in Agrotain^®), the urease inhibitor 2-Nitrophenyl phosphoric triamide (2-NPT, contained in Piazur^®), the nitrification inhibitors dicyandiamide (DCD) and triazole (contained in Alzon^®), and NBPT combined with DCD (SuperU^®). Soil pH ranged from 6 to 8, the soil moisture content ranged from 50% to 100% of field capacity, and the soil temperature ranged from 5°C to 25°C.