Effects of Nitrogen Source, Application Timing, and Dicyandiamide on Furrow‐Irrigated Rice

Furrow‐irrigated rice (Oryza saliva L.) is a cost‐reducing water delivery alternative to traditional flooded rice management. However, N transformations in intermittently irrigated fields will differ from those under seasonal flooding. This study was conducted to evaluate N sources and application timings with respect to yield and N transformations for furrow‐irrigated rice. Treatment responses of furrow rice to urea, urea‐NH4NO3 (UAN), (NH4)2SO4 (AS), and sulfur‐coated urea (SCU), were investigated with and without the nitrification inhibitor dicyandiamide (DCD). Nitrogen was applied at 180 lb/acre at 4 wk after planting (4WAP) with and without DCD; a 1:1:1 ratio 4WAP, panicle differentiation (PD), and 14 post‐PD; and a 4:1:1 ratio at 4WAP, PD, and 14 d post‐PD. Soil and plant samples were analyzed for N concentrations at tillering and heading. Yields ranged from 94 to 134 bu/acre in 1988, and 69 to 133 bu/acre in 1989. The SCU fertilizer was an excellent N source when multiple applications were avoided. The 1:1:1 application timing produced poor yields by limiting early vegetative growth across all N sources. Although DCD treatments produced relatively high yields, significantly greater yields obtained with DCD occurred only with the AS source in 1988. Plant N concentrations were stimulated by UAN treatments, followed by urea, AS, and SCU sources. In each year, the current N recommendation for flooded rice (180 lb N/acre urea, applied in a 4:1:1 ratio) produced yields in the highest group. Thus, optimum N sources and application timings were found to be similar to those of flooded rice.