Influence of Nitrogen Source on Ammonia Volatilization Loss In Delayed-Flood Rice.

Increasing N use efficiency in rice production is important for continued sustainability.  Field experiments were conducted in 2009 and 2010 at Stoneville, MS, to quantify N loss via ammonia volatilization and determine the grain yield effects for various N sources and application timing on clay textured soil.  Both experiments were arranged in an RCB design.  Yield data were subjected to ANOVA and means separated using Fisher’s LSD _(0.05).  Non-linear procedures were used to model cumulative volatilization losses.  Nitrogen sources included: urea, Agrotain^® treated urea, Super-U^®, ammonium sulfate (AMS), and AMS + urea. For yield evaluations, N fertilizer was applied at a rate of 168 kg ha^-1 at 10, 7, 4 and 1 day before permanent flood establishment (dbf).  To quantify the amount of volatilization losses, a semi-open static system was used. Ammonia volatilization was measured for 21 days following the application that was made 14 days prior to permanent flood establishment. Cumulative N loss varied by N source. Urea, AMS + urea, AMS, Super-U, and Agrotain resulted in 9.89, 9.45, 5.51, 5.11, and 3.71% loss, respectively. The time at which N loss reached a plateau also was influenced by N source. Nitrogen loss for urea, AMS + urea, AMS, Super-U, and Agrotain reached a plateau at 5.5, 4.2, 4.1, 8.1, 8.4 days, respectively. Nitrogen source did not affect rice grain yield in 2009 and 2010. This can be explained by the fact that approximately 10% N loss was the maximum. In 2010, rice grain yields were approximately 5% less when fertilizer was applied 10 dbf. These data suggest that N loss via ammonia volatilization on clay textured soil is minimal; however, sources are available to minimize N loss via ammonia volatilization.  Furthermore, other loss mechanisms such as nitrification/denitrification should be investigated to increase N use efficiency in delayed-flood rice production.