A field study was conducted to evaluate the effects of the addition of two different urease inhibitors on the volatilization of NH3-N from top dressed ammonia sources on winter wheat and dent corn. Urease inhibitors tested were N-Yield~(TM) and Agrotain~R. Plots were treated with compost, compost treated with N-Yield~(TM), urea urea treated with N-Yield~(TM), urea treated with Agrotain~R, or control (no fertilizer or urease inhibitor was applied). At maturity, above-ground biomass was separated intograin and straw, with each constituent evaluated for total N, P, K and S. Total N concentrations in wheat straw ranged from 0.64% in the control to 1.36% in the treatment containing urea treated with N-Yield~(TM). Total N concentrations in wheat grain ranged from 2.09% in the control to 3.52% in the treatment containing urea with N-Yield~(TM). Similarly, N concentrations in the corn stover ranged from 0.81% in the compost treatment to 1.80% in the treatment containing urea treated with Agrotain~R. TotalP concentrations in wheat straw ranged from 0.08% in the control to 0.17% in the treatment containing urea treated with N-Yield~(TM). Total P concentrations in wheat grain ranged from 0.47% in the control to 0.57% in the treatment containing compost with N-Yield~(TM). However, the data analyzed in this study suggest that, in field conditions, while the application of urea fertilizer greatly increases N concentrations in wheat and corn, the addition of NBPT (whether Agrotain~R or N-Yield~(TM)) to urea before field application does not significantly increase N concentrations over that of urea alone.
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