Date of Graduation


Document Type


Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level



Crop, Soil & Environmental Sciences


Nathan Slaton

Committee Member

Trenton Roberts

Second Committee Member

Jarrod Hardke

Third Committee Member

Edward Gbur


Development, Nitrogen, Preflood, Rice, Timing, Yield


Urea-N fertilizer is typically applied at the 5-leaf stage to rice (Oryza sativa L.) grown in a dry-seeded, delayed-flood production system. How long the preflood-N can be delayed without adverse effects on yield potential is poorly understood. The research objective was to determine the effects of preflood-N application and flood establishment timing on aboveground-N content, 50% heading, yield components, and grain yield. Trials were established on silt loam soils at the Pine Tree Research Station (PTRS) and Rice Research and Extension Center (RREC) during 2015 and 2016. Urea-N was applied at 0, 45, 90, 135, and 180 kg N ha-1 on five to seven different dates with applications beginning near the 3-leaf stage and ranging from 127-1035 growing degree units (GDU). The current optimal time to apply preflood-N is defined as 195-310 GDU. Aboveground-N content at each site-year, 50% heading for each cultivar and relative grain yield and yield components at each location were regressed across cumulative GDU at the time of N application allowing for linear and quadratic terms with coefficients depending on N rate. Aboveground-N content increased as fertilization and flooding were delayed. Spikelets panicle-1, % filled spikelets, and effective tillers were affected by the fertilization delay at all locations. At the PTRS relative grain yield declined when fertilization and flooding occurred beyond 531 GDU suggesting that this is the point when the yield components could no longer compensate for one another. The delay in fertilization and flooding delayed 50% heading for all cultivars. Results from this study indicated that rice grain yield is affected when fertilization and flooding is delayed beyond 531 GDU, which is approximately 13 to 20 d beyond the current recommended time to apply preflood-N and 6 d beyond the current final recommended time to apply preflood-N average for the cultivars assessed in this study.