Five rates of N fertilizer as urea as 0 (R1), 60 (R2), 90 (R3), 120 (R4), 150 (R5) kg N ha−1 were applied, in three split-application: basal 50% at preplanting, topdressing 35% at tillering and 15% at booting stages, respectively. The experiment was laid out in a randomly complete block design with four replications for each N treatment.