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

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Abstract
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 Inceprisol (Typic Haplaquepts). The 1,200 mg N application timing was: i) total at sowing (T1); ii) one‐third at sowing+one‐third at active tillering + one‐third at panicle initiation (T2); iii) one‐third at sowing + one‐third at panicle initiation + one third at booting (T3); iv) one‐third at planting + one‐third at panicle initiation + one‐third at flowering (T4); v) zero at sowing+one‐half at the initiation of tillering + one‐half at panicle initiation (T5); and vi) zero at sowing + one‐third at the initiation of tillering + one‐third at booting + one‐third at flowering (T6). 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 T1 treatment, followed by the T2 and T5 treatments. Treatments T4 and T6 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.