Effect of the Amount and Timing of Ammonium Sulfate Single Top-dressing Application on Growth and Yield of Akitakomachi Rice (Oryza sativa L.)

The effect of the amount and the timing of single top-dressing application of Ammonium sulfate fertilizer on the growth and yield of Akitakomachi rice (Oryza sativa L.) was investigated in this study. Two amounts (20kg.ha-1 and 50kg.ha-1) of Ammonium sulfate ((NH4)2SO4) fertilizer were applied at three timings;14 days after transplanting, panicle initiation, and flowering respectively, giving six treatments (14DAT:20, 14DAT:50, PI:20, PI:50, FL:20 & FL:50). A Randomized Complete Block Design (RCBD) with three replications was used. Growth data were collected on plant length, number of tillers and leaf color, and calculated yield and yield components were determined. Plant length was significantly higher in 14DAT:50 and PI:50, and lowest in FL:20 and FL:50. Tiller number was higher in 14DAT:50 compared to the other treatments. 14DAT:50 and PI:50 produced the highest number of panicles per m2. PI:20 and PI:50 had the highest number of spikelets per panicle. The 1000 grains weight was highest in PI:50 and lowest  in 14DAT:50. The highest yields were obtained in 14DAT:50 and PI:50, while FL:20 and FL:50 produced the lowest yields. The results showed that for nitrogen (N) single top-dressing application, high amounts increase both the plant growth and the grain yield if the application is done at vegetative stage or at panicle initiation stage. However, if the nitrogen (N) amount is too high, there exist the risk that the plants may lodge.