Abstract
The study was carried out at the Agronomy Field Laboratory, Bangladesh Agricultural University (BAU), Mymensingh (AEZ-9) and Sankiduary village of Purbadhala Upazilla, Netrakona (AEZ-22) during boro season of 2010-11 and 2011-12 to determine the effect of varieties, transplanting date and nitrogen management on the growth and yield of rice. The study also simulated the impact of climate change in relation to temperature and CO₂ on the yield of boro rice under various transplanting dates using the modified RIBHAB rice model. Experiment 1 was conducted with twelve varieties viz. BRRI hybrid dhan1, BRRI hybrid dhan2, BRRI hybrid dhan3, SL8-H (Super Hybrid), BRRI dhan28, BRRI dhan29, BRRI dhan45, BRRI dhan47, BRRI dhan50, Binadhan-6, Binadhan-5, Binadhan-8 and three transplanting dates viz. 1 January, 15 January and 30 January in the two locations. The results of the experiment revealed that variety and transplanting date had significant influence on growth parameters viz. plant height, number of tillers hill⁻¹, leaf area index and dry matter production as measured at 20, 30, 40, 50 and 60 days after transplanting (DAT) and eventually on yield and yield contributing characters. The highest grain yield in both locations was found from the interaction of BRRI dhan29 planted on 01 January planting (9.34 t ha⁻¹ and 8.76 t ha⁻¹) whereas the lowest yield was found in the interaction of BRRI dhan47 planted on 30 January (4.93 t ha⁻¹ and 4.55 t ha⁻¹). Experiment 2 was conducted at the Agronomy Field Laboratory of the Bangladesh Agricultural University, Mymensingh with five rice varieties viz. BRRI hybriddhan2, BRRI hybriddhan3, SL8-H (Super Hybrid), BRRI dhan29 and Binadhan-5) and six fertilizer treatments viz. control (farmers' practice), 20 kg N ha⁻¹ (Applied as prilled urea in three equal splits), 95 kg N ha⁻¹ (based on LCC), 80 kg N ha⁻¹ (applied as USG), 120 kg N ha⁻¹ (applied 80% N from Prilled Urea and 20% N from compost) and 120 kg N ha⁻¹ (applied 80% N from Prilled Urea and 20% N from cowdung). Variety, level, and source of nitrogen had significant influence on growth parameters viz. plant height, leaf area, LAI, total dry matter, tiller number and yield and yield parameters such as effective tiller hill⁻¹, number of grain panicle⁻¹, thousand grain weight, grain yield and straw yield. The highest number of tillers hill⁻¹ (13.62), effective tillers hill⁻¹ (11.47) were obtained from BRRI dhan29. But BRRI hybrid dhan3 and SL8-H produced the highest grain yield (8.5 t ha⁻¹ and 8.83 t ha⁻¹) due to their bolder grain (1000-grain weight BRRI hybrid dhan3: 31.06 g and SL8-H: 28.6 g) compared to BRRI dhan29 (22.98 g). On the other hand, the lowest yield and yield parameters were obtained from Binadhan-5. The highest grain yield was found (9.43 t ha⁻¹) in the interaction of BRRI hybriddhan3 with 120 kg N ha⁻¹ (in three equal splits) and the lowest grain yield was observed (6.42 t ha⁻¹) in the interaction of Binadhan-5 and farmers practice. In economic analysis, the highest gross return, gross margin, net return hectare⁻¹ of boro rice was observed in 80 kg N ha⁻¹ as USG treatment (Tk. 153532, Tk103949, Tk 88966). The highest benefit-cost ratio of boro rice production ha⁻¹ was observed in 80 kg N ha⁻¹ as USG treatment (2.38). The impact of climate change in terms of CO₂ and temperature on the yield of boro rice during 2030 and 2070 was predicted using the modified RIBHAB rice model. Based on the prediction the probable yield loss would be 16%, 21% and 28% at 01 January, 15 January and 30 January transplanting, respectively in 2030, but in 2070 yield loss would be 25%, 68% and 45% in the corresponding dates. The suitable transplanting date for boro rice were suggested to be 15 January for 2030 and 15 April for 2070. The simulation predicts that boro rice transplanting on 15 January would be better than 30 January in 2030. Suitable transplanting date for boro rice in Bangladesh would be delayed with further progress of time and in 2070, 15 April would be the most appropriate time for boro transplanting in Bangladesh.