| The availability of a controlled-release N fertilizer suitable for preplant application to rice (Oryza sativa L.) grown using a delayed-flood system would offer producers an alternative N-fertilization method with potential for reducing aerial application costs of N fertilization. However, the N release profile of a polymer-coated urea (PCU) that allows for efficient N uptake when applied preplant is unknown. Research objectives were to compare grain yield and N uptake of rice receiving preplant incorporated PCU with urea applied preflood and characterize the N-release of several PCU fertilizers, including Environmentally Smart N (ESN). Field and laboratory incubation experiments utilized a buried-bag method to determine N release across time of selected PCU fertilizers as affected by soil series, moisture, and temperature. Field experiments, conducted at multiple sites, compared yield and N uptake of rice fertilized preplant with PCU to preflood application of urea-N across N rates from 0 to 168 kg N ha-1. Soil series and moisture had a nominal influence on N release from ESN. Soil temperature had the greatest influence on N release rate, which increased as temperature increased. By 40 d after application, ESN contained 13 and 14% of the initial N content when incubated at 20 and 25°C, respectively. Comparison of field and laboratory incubation results showed little difference in N retained in PCU prills across time, suggesting that laboratory incubations could accurately model N release in the field. Nitrogen release from the evaluated PCU fertilizers was either too fast or slow to provide adequate N for optimum rice growth and yield in the delayed-flood system. Rice grain yield and N uptake were lower for rice receiving PCU preplant compared to rice receiving urea-N preflood. Fertilizer-N recovery at panicle differentiation was never >35% for rice receiving preplant-applied PCU and averaged 73% for urea-N applied preflood. Rice grain yields were numerically greater for rice receiving urea preflood, when compared to rice receiving preplant PCU, at all but one site-year. Overall, the selected PCU fertilizers were not suitable, alternative N sources for delayed-flood rice production, but may he suitable for other crops grown in the Midsouth USA. |
