Effect of Phenylphosphorodiamidate on Immobilization and Ammonia Volatilization

Abstract Laboratory incubation experiments were conducted to evaluate the ability of the urease inhibitor phenylphosphorodiamidate (PPD) to reduce NH3 volatilization and immobilization of urea (100 mg N kg−1 of soil). Application of 20 mg PPD kg−1 of soil effectively inhibited urea hydrolysis for approximately 4 d in both soil and oat straw‐amended soil systems. This delayed urea hydrolysis reduced NH3 losses after 7 d from 82 to 19% in the straw‐amended soil, and from 26 to 14% in the soil system. When urea was applied to soil incubated in closed vessels, only 80% of the applied urea could be recovered as inorganic N after 3 d of incubation. This apparent immobilization of N was prevented for 7 d by application of PPD. Immobilization of N in the straw‐amended soil exceeded 40% within 7 d, but the onset of these losses was delayed for at least 3 d by PPD. These results demonstrate that losses of surface‐applied urea via both NH3 volatilization and immobilization can be prevented by application of an effective urease inhibitor.