Effect of Urease Inhibitors On Ammonia Volatilization.

Urea is the most important source of nitrogen (N) fertilizer in the United States.  Urea’s high N content (46%) make it an ideal N source, but the process of hydrolysis makes it vulnerable to N loss through volatilization.  Incorporation by either mechanical or irrigation has been the accepted method used to minimize volatilization.  Since mechanical incorporation is not always possible, a urease inhibitor can prolong the interval between application and irrigation incorporation to minimize ammonia loss.  Field scale research is limited that quantifies the effectiveness of urease inhibitors and consequential ammonia loss.  Two trials were conducted on different urease inhibitor products.  One comparing urea, urea coated with N-(n-butyl) thiophosphoric triamide (NBPT) trade name Agrotain, and ammonium sulfate was performed in the fall on Kentucky Bluegrass.  The second compared urea, urea treated with NBPT, and urea treated with an organic acid complex which was malic acid with copolymers (MA) was performed in the spring on winter wheat with irrigation rates of 0.00, 2.54, and 12.7 mm.  The Kentucky Bluegrass fields showed upward of 15.3% of urea applied being lost as ammonia on a 5.9 and 6.5 pH sandy soils.  The urease inhibitor Agrotain reduced ammonia loss by 71.8%, when compared to urea and had a similar loss as ammonium sulfate.  MA and urea had similar ammonia loss on the Winter Wheat at both 0.00 and 2.54 mm irrigation rates with loss rates ranging from 60.06% to 53.91 % of N applied.  MA and urea also had similar N losses at the 12.7 mm irrigation rate, 17.31 to 8.11 % N, respectively.  The losses at 12.7 mm were less than at the 0.00 and 2.54 mm irrigation rates.  The NBPT N losses ranged from 6.24% to 3.17 % N applied across all three irrigation rates, lower than the urea and MA at 0.00 and 2.54 mm irrigation rates, but not different than urea and MA at 12.7 mm.  NBPT was able to reduce ammonia loss by volatilization when incorporation by irrigation was not applied at greater than 12.7 mm.  MA showed no inhibition of urease.  The application of 12.7 mm of irrigation water was adequate to limit N loss.  Three weeks after N application the urea and MA plots showed no difference in urease activity between each other.  The urease activity in the NBPT plots was significantly lower than either the MA and urea treatments.