Aman, Gypsum, Split-plot, Swarna, Yield component
Experimental Site and Soil-The experiment were conducted at Moddho Jutkhali, Subornochar upazila situated in Noakhali district, the southern part of Bangladesh (22°26? to 22°56? N latitude and 90°24? to 90°54? E longitude) at an altitude of 9 m above mean sea level. The experimental site belongs to the Young Meghna Estuarine Floodplain Agro-ecological zone (AEZ-18). It occupies young alluvial land in and adjoining the Meghna estuary. The soil of the experimental plot was silt loam with low organic carbon and low available nitrogen with alkaline reaction. Experimental Treatments and Design-The experiment was laid out in a Split-plot design with two factors followed by three replications. The treatments comprised of three aman rice varieties viz., Swarna (V1), BRRI dhan52 (V2) and Binadhan-7 (V3) and three levels of gypsum viz., 0, 75 and 150 kg gypsum ha-1. The size of the unit plot was 10 m2 (4 m × 2.5 m) and the spaces between blocks and plots were 1 m and 0.5 m, respectively. Various levels of gypsum were given in the main plots whereas different varieties were transplanted in the sub-plots. Swarna is an Indian variety adapted to the Southern region of Bangladesh. The grain type is short bold with brown husk. The duration of the variety is 150-155 days and it has a yield potential of 5.6 to 6.0 ton ha-1. It can be cultivated in aman season in the coastal delayed area and low rainfed area. This rice variety is released by the Bangladesh Rice Research Institute (BRRI) in the year of 2010. Duration is 140-145 days. The panicle is heavy with a high grain number. Grain weight is 22 g per 1000-grains. The quality of the grain is medium to slender. The yield potential of the variety is 4.5 to 5 ton ha-1. A special feature of this variety is that it can survive under the flooded conditions for about 15 days. The culm of the plant is strong and the plant is slightly photosensitive. It is a short duration and high yielding transplant aman rice variety released by the Bangladesh Institute of Nuclear Agriculture (BINA) in 2007. Crop duration is about 110-120 days from seed to seed. As the variety is early maturing facilitate rabi crop cultivation like potato, mustard, wheat, etc. It is more tolerant to sheath blight, leaf blight and stem rot. Yield potential is about 5 to 5.5 ton ha-1. It has a long fine and bright color grain. Sprouted rice seeds were sown in the wet nursery bed on 23 June 2017. Thirty-three days old seedlings were transplanted in the puddled main field using two seedlings hill−1 on 26 July 2017. Row to row and plant to plant spacing adopted for transplanting was 25 cm and 15 cm, respectively. The recommended dose of 160- 50-70-5 kg ha-1 urea, triple superphosphate, muriate of potash, and zinc sulfate, respectively were applied uniformly to all the plots. All other fertilizers except urea and gypsum were applied as basal dose during final land preparation. Gypsum was applied as per the treatments. Nitrogen was applied in the form of urea in three equal splits-one at basal, one at tillering and the final one at the panicle initiation stage. Intercultural operations were done as and when necessary. Weeds were removed from the plots manually twice at 30 and 45 days after transplanting (DAT) and the plots were kept weed-free. The crop was raised as rainfed. At the time of transplanting, a thin film of water was maintained for the easy establishment of seedlings. In general, 6-9 cm stagnant water was present in the field during most part of its growth. From the panicle initiation stage, 5 cm depth of water was maintained up to the dough stage. After the dough stage, water was gradually drained out to facilitate proper maturity and easy harvest. No major incidence of pests and diseases was observed except minor incidence of leaf folder which was managed by spraying chlorpyriphos @ 2 ml L-1 of water. Five hills (excluding border hills) were randomly selected from each unit plot prior to harvest for recording data on plant characters, yield and yield components. The date of harvesting was determined when 90% of the grains became golden yellow in color. For individual plots, the whole plot was manually harvested from the ground level to take grain and straw yields. The harvested crop was then threshed, cleaned and dried to a moisture content of 14% (for grain). Straws were sun-dried properly. The weight of grain and straw were recorded and converted into t ha−1.