Grain Yield and Milling Quality Response of Two Rice Cultivars to Top‐Dress Nitrogen Application Timings

Combinations of two vegetative N application schemes (single pre-flood [SPF]) and two-way split [2WS]) and five top-dress (TD) N timings (internode elongation [IE], IE+7, 14, 21, and 28 d) were tested for 'Cocodrie' and 'Wells' rice. When averaged across TD timings, the average grain yield for Cocodrie was 9142 kg ha -1 when the SPF scheme was used, compared with 8736 kg ha -1 for the 2WS scheme. Whole and total milled rice percentage showed a quadratic response to TD timing and was greatest when the TD application was made at IE+28 d for Cocodrie; however, only the early vegetative N application scheme affected the net return, which, when averaged across TD timings, was $75 ha -1 greater when the SPF scheme was used. When N was top-dressed at the IE timing, whole milled rice was 52.9% with the SPF scheme, compared with 49.8% with the 2WS scheme. In addition, where the SPF scheme was used, whole milled rice responded quadratically to TD timing compared with linearly when the 2WS scheme was used. Sensitivity analyses indicated that at three N prices ($0.16, $0.33, and $0.48 kg -1 ), the relative difference in net returns among treatment combinations were not changed. Rice grain yields for semi-dwarf cultivars respond more favorably to a higher percentage of the total N being applied pre-flood. Growers should implement N fertilizer practices that produce the highest economic grain yield, which for Cocodrie is to use the SPF vegetative N application scheme regardless of the TD N timing.