An experiment was conducted in Agronomy farm, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh from December 2011 to May 2012. Experiment consisted four different aged seedlings viz. A1: 12 days old seedling, A2: 14 days old seedling, A3: 16 days old seedling and A4: 30 days old seedling following Completely Randomized Block Design with three replication. The seeds of BRRI dhan50 were collected from Bangladesh Rice Research Institute (BRRI), Joydebpur, Gazipur. The fertilizers N, P, K, S, Zn and B in the form of urea (150 kg ha-1), TSP (100 kg ha-1), MP (80 kg ha-1), gypsum (60 kg ha-1), zinc sulphate (10 kg ha-1) and borax (10 kgha-1) respectively were applied. Entire amount of TSP, MP, gypsum, zinc sulphate and borax were applied during final preparation of plot land. Mixture of cowdung and compost (10 tha-1) was applied during 15 days before transplantation. Urea was applied in three equal installments at after recovery, tillering and before panicle initiation. Data were collected on plant height, number of tillers/hill, leaf area index, dry matter/hill, effective tillers/hill, ineffective tillers/hill, panicle length, filled grains/panicle, unfilled grains/panicle, weight of 1000-grains, grain yield, straw yield, biological yield, harvest index, weed population/m2 and weed dry matter/m2. Leaf area index measured manually and final data calculated multiplying by a correction factor 0.75. Collected plants including roots, leaves, grain and straw were oven dried at 700C for 72 hours then transferred into desiccator and allowed to cool down at room temperature, final weight was taken and converted into dry matter content/hill. The biological yield was calculated with the following formula:
Biological yield = Grain yield + Straw yield.
Harvest index was calculated by following formula
HI (%) = {Economic yield (grain weight) ÷ Biological yield (Total dry weight)} × 100
Collected data were statistically analyzed using IRRISTAT software to observe the significant difference among the treatments. The mean values of all the characters were calculated and analysis of variance was performed. The significance of the difference among the treatment means was estimated by the Least Significant Difference (LSD) test at 5% level of probability.