Ammonia Volatilization from Tall Fescue As Affected By Urease Inhibitors.

New N fertilizers with added urease inhibitors have recently been introduced to the turfgrass market.  Typically urea to which various inhibitors have been added, the efficacy of such materials to reduce ammonia loss in turf systems via volatilization is not well known.  Thus, the objective of this project was to evaluate the effectiveness of three urease inhibitors for their ability to reduce ammonia loss from turf.  Four treatments (urea, urea + dicyandiamide (DCD)/ N-(n-butyl) thiophosporic triamid (NBPT), urea + maleic itaconic co-polymer, and urea + Ca-heteropolysacharides Cl) were applied at an N rate of 7.3 g m^-2 to the surface of a 10 cm diameter tall fescue plugs contained in 1 L jars.  Jars were sealed, and NH₃ volatilization over 11 days (measured every other day) was measured via boric acid trapping.  No additional water was added during this time.  Each treatment was replicated 4 times, and the entire experiment was conducted thrice.  In every case the only urease inhibitor which significantly reduced ammonia loss was urea + DCD/NBPT, and this reduction was likely due to the presence of the urease inhibitor NPBT.  Average cumulative N loss (as a percent of N applied) in all other treatments was 22% of N applied, while average cumulative ammonia loss from turf to which urea + DCD/NBPT had been applied was 9%.  Reductions in ammonia loss were most evident in the first 5 days of data collection, and differences due to source were small thereafter.