Yield and yield components of lowland rice as influenced by timing of nitrogen fertilization

Insufficient nitrogen (N) supply is an important constraint to productivity of lowland rice (Oryza sativa L.), and there is limited information available on optimum timing of N application for lowland rice. To determine the effects of timing of ammonium sulphate application on yield, yield components, and N-use efficiency of lowland rice, a greenhouse experiment was conducted on an Inceptisol (Typic Haplaquepts). The 1,200 mg N application timing was: i) total at sowing (T-1); ii) one-third at sowing + one-third at active tillering + one-third at panicle initiation (T-2); iii) one-third at sowing + one-third at panicle initiation + one third at booting (T-3); iv) one-third at planting + one-third at panicle initiation + one-third at flowering (T-4); v) zero at sowing + one-half at the initiation of tillering + one-half at panicle initiation (T-5); and vi) zero at sowing + one-third at the initiation of tillering + one-third at booting + one-third at flowering (T-6). Dry matter, grain yield, N uptake, and N-use efficiency were significantly affected with timing of N application treatments. Maximum grain yield was obtained with the T-1 treatment, followed by the T-2 and T-5 treatments. Treatments T-4 and T-6 produced minimum grain yields. Nitrogen treatments had highly significant (P<0.001) effects on the number of panicles, followed by filled (P<0.01) and unfilled (P<0.05) spikelets. The number of panicles was the most important component of yield, accounting for about 87% of the variation in yield.