Bobby Golden1, Nathan Slaton2, Russell DeLong2, and Richard Norman2. (1) University of Arkansas, 1366 W Altheimer Drive, Fayetteville, AR 72704, (2) Univ of Arkansas, 1366 W Altheimer Dr, Fayetteville, AR 72704
Rice (Oryza sativa L.) grown in the direct-seeded, delayed-flood system relies on aerial application of N-fertilizer. Applying N-fertilizer with ground equipment before seeding would reduce N-application costs. The objective was to compare N uptake and yield of rice receiving preplant applied polymer-coated urea fertilizers with the standard practice of urea applied preflood to rice grown in the delayed-flood system. In 2006, three experiments were established on silt loams. Three polymer-coated urea fertilizers (ESN, 44% N; and Duration type III and V, 43% N; Agrium Inc., Calgary, AB, Canada) were broadcast at total-N rates ranging from 34 to 168 kg N ha-1 immediately before seeding. Before flooding (31-41 d after planting), urea was applied at the same total-N rates as the polymer-coated fertilizers. Total, aboveground N uptake was determined near the panicle differentiation (PD) stage for treatments receiving 134 kg N ha-1. Each experiment was a randomized complete block with a 4 (N source) by 5 (N rate) factorial treatment arrangement plus an unfertilized control. Regression analyses showed the N source by nonlinear N rate interaction was significant for grain yield. The linear and nonlinear slope coefficients were always similar among polymer-coated sources among sites and significantly lower than coefficients for urea applied preflood. For urea (preflood), rice yields increased nonlinearly as N rate increased with maximal yields produced with 140-168 kg N ha-1. The nonlinear coefficients for polymer-coated sources (preplant) were not different from zero indicating yields increased linearly as N rate increased. For each N rate, grain yields were always greatest when urea was the N source. Nitrogen fertilizer recovery at PD was always greater for rice receiving urea preflood (mean = 66%) compared with the polymer-coated urea sources (mean range = 10-20%). The evaluated preplant applied polymer-coated fertilizers were not suitable, alternative N sources compared with urea applied preflood.
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