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 availa ble on optimum timing of N application for lowland rice. To determine the e ffects of timing of ammonium sulphate application on yield, yield component s, and N-use efficiency of lowland rice, a greenhouse experiment was conduc ted 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 acti ve tillering + one-third at panicle initiation (T-2); iii) one-third at sow ing + one-third at panicle initiation + one third at booting (T-3); iv) one -third at planting + one-third at panicle initiation + one-third at floweri ng (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 th e initiation of tillering + one-third at booting + one-third at flowering ( T-6). Dry matter, grain yield, N uptake, and N-use efficiency were signific antly 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 treatment s. Treatments T-4 and T-6 produced minimum grain yields. Nitrogen treatment s had highly significant (P<0.001) effects on the number of panicles, follo wed by filled (P<0.01) and unfilled (P<0.05) spikelets. The number of panic les was the most important component of yield, accounting for about 87% of the variation in yield.