Abstract
Eight experiments were carried out at the Bangladesh Rice Research Institute Farm, Gazipur from 1998 to 2001. Initially 26 varieties of modern aromatic, traditional and Basmati rice (aromatic and non aromatic) were transplanted both in the Aman and Boro seasons for screening the varieties having high yield potential. Finally, 12 varieties were screened having high yield potential; four varieties from each group of Basmati, traditional and modern aromatic rices based on growth, duration and yield.
Twelve screened varieties were transplanted from 22 July to 7 October in Aman season and 10 December to 25 January in Boro season at 15-day intervals to find out the optimum planting date. Moreover, these varieties were tested at varying levels of nitrogen 0, 25, 50, 75 and 100 kg N ha1 in the Aman and 0, 35, 70, 105 and 140 kg N ha1 in the Boro seasons to find out the optimum level of nitrogen and the nitrogen responsive varieties. Finally, most promising six varieties were selected to transplant in Boro season with water stress imposed at vegetative, reproductive and grain filling stages and at varying levels of nitrogen 0, 70, 105 and 140 kg N ha' to determine the critical growth stage where water stress affect on yield loss.
The plant height, tiller number, dry matter, grain and straw yield and yield components were varied significantly due to transplanting at variable dates both in the Aman and the Boro seasons. The optimum time of planting of fine rice was 9-11 August in the Aman and 10 December in the Boro seasons. Compared to 22 August planting, the grain yields decreased by 22, 13, 8, 30 and 66% when planted on 22 July, 7 August, 7 September, 22 September and 7 October, respectively in the Aman season. Transplanted in optimum time the Basmati PNR, BRRI dhan37 and BRRI dhan38 gave higher grain yield. But in late planted (beyond 7 September), most of the traditional and Basmati rice gave higher grain yield over modern rice. The poor grain yield of traditional rice in early-planted was due to higher percentage of spikelet sterility. The fine rice varieties responded well with the optimum level of 69-70 kg N ha1 in the Aman and 135 kg N ha1 in Boro seasons. BRRI dhan38, BRRI dhan37 and BR5 and the Basmati PNR responded well with the optimum level of 43, 81, 88 and 119 kg N ha1 in the Aman and 144, 160, 181 and 137 kg N ha1 in Boro seasons. The higher number of panicles m2, lower spikelet sterility and heavier individual grain contributed to increase grain yield of the varieties. The high tiller productive Chinigura and the taller plant Kalijira gave comparable yield with modern rice BRRI dhan37 and BRRI dhan38 at the lower levels of nitrogen. But at the higher level of nitrogen the traditional rice gave lower grain yield due to the higher percentage of spikelet sterility. The better grain quality as well as aroma content of Basmati370 and BRRI dhan37were higher (strong) of 7 September transplanted crop in Aman season with the lower level of nitrogen. Crop affected by water stress at the vegetative growth stage reduced effective tillers and at the reproductive stage increased spikelet sterility resulting in reduction of grain yield. It is, therefore, suggested to transplant potential fine rice 9-11 August in Aman and 10 December in Boro seasons. The application of optimum level of nitrogen 69-70 kg ha' in Aman and 135 kg ha1 in Boro seasons is enough to obtain higher grain yield. The irrigation would be ensured at the vegetative stage to increase effective tillers and at the reproductive stage to decrease spikelet sterility to avoid yield loss.