Assessment of Urea Stabilizers Applied Preflood to Delayed-Flood Rice.

Current and projected N fertilizer prices have renewed an interest in fertilizer stabilization methods to increase efficiency and productivity. Two of the most common approaches to circumvent N losses from urea fertilizers are the enzymatic inhibition of urea hydrolysis and nitrification. Delayed-flood rice relies on large inputs of N fertilizer applied immediately prior the establishment of a permanent flood which are prone to losses via ammonia volatilization and nitrification. Field studies were conducted in Arkansas and Mississippi to investigate the potential benefits of Nutrisphere as an emerging urea stabilization product. Urea, ammonium sulfate and Agrotain coated urea or Nutrisphere coated urea were applied at different times prior to establishment of a permanent flood. Rice grain yield was largest when ammonium sulfate and Agrotain coated urea were used. There were no significant differences between Nutrisphere coated urea and urea when applied 5 and 10 days prior to flooding. In order to evaluate the products solely on the mechanism of enzymatic inhibition a laboratory study was initiated. Aerobic incubation was utilized to determine the effects of Agrotain and Nutrisphere on urease activity and the resultant losses due to ammonia volatilization. Super U was also included in the laboratory incubation to evaluate the potential of Nutrisphere as a nitrification inhibitor. There were no significant differences in ammonia volatilization between urea and Nutrisphere coated urea following aerobic incubation. Nitrification was compared following the aerobic incubation of which Super U had the lowest nitrate production. Urea and Nutrisphere coated urea were not significantly different than one another and resulted in the largest production of nitrate. Results of both the field and laboratory experiments demonstrate the inability of Nutrisphere to inhibit ammonia volatilization or nitrification, thus it is not recommended as a urea stabilization product to increase fertilizer efficiency.