Nitrogen Content in Floodwater of Drill-Seeded, Delayed Flood Rice Following Urea Fertilization.

Nitrogen (N) fertilizer has the potential to enter surface waters via runoff from rice [Oryza sativa (L.)] fields.  This study was conducted to determine the days after fertilizing with urea that floodwater should be held to minimize N loss via runoff.  The effects of fertilizer N rate, fertilizer N application time, and floodwater temperature on the extent and persistence of urea, ammonium, and nitrate in rice floodwater were examined with a dry-seeded, delayed flood cultural system at Stuttgart, AR on a Dewitt silt loam (fine, smectic, thermic Typic Albaqualf).  Preflood N fertilizer persisted in the floodwater for more than one week after application and flooding, while midseason N fertilizer remained for 5 days.  Increased N fertilizer rate and decreased floodwater temperature appears to lengthen the persistence of N in rice floodwater.  Recommendations regarding the length of time floodwater should be held after fertilization with urea may need to account for these factors.