Abstract
Ten experiments were conducted at the Department of Agronomy, Bangladesh Agricultural University, Mymensingh and Sher-e-Bangla Agricultural University, Dhaka during 1999-2000, 2000-2001 and 2001- 2002 boro seasons to study the performance of rice under cold night temperature treatments imposed at of flower initiation and to observe the influence/agronomic management on the spikelet sterility and yield of rice. The results show that low night temperatures (18°C and 16°C) for rice varieties BRRI dhan29 and Sonarbanglal promoted spikelet sterility from 26.78 to 32.92% and decreased grain yield from 5.54 .0 12.89%. Several forms of hypoplasia and hyperplasia of the reproductive organs of rice spikelets were identified with low temperature. A test involving twenty-four varieties against cold night temperatures showed that spikelet sterility ranged from 5 to 69% followed by trends in grain yield reduction. On the basis of increasing spikelet sterility and grain yield reduction, a gradation was made with 5 varieties as susceptible (BR2, BR3, BR18, BRRI dhan29 and Alokdhan), 14 varieties as moderately resistant (BR7, BR8, BR9, BR14, BR15, BR16, BR19, BRRI dhan28, BRRI dhan35, BINA dhan5, BINA dhan6, Sonarbanglal, Sonarbangla5 and Sonarbangla6) and 5 other varieties as resistant (BR1, BR6, BR12, BR17 and BRRI dhan36).
As means of improving spikelet sterility, 20cmx15cm spacing was found superior to each of closer and wider spacings. The hybrid rice Sonarbanglal was found moderately resistant to sterility (15.91 to 23.87%), while BRRI dhan29 was found much vulnerable to sterility (24.07 to 34.44%) under different transplanting dates. The 20 December transplanting was found suitable for both varieties in reducing sterility and hence, increasing grain yield. Seedling age of 30-40 days for Sonarbanglal and 40-50 days for BRRI dhan29 showed the better performance in terms of producing the higher grain yield by reducing spikelet sterility. A study with micro-nutrients revealed that the use of four micro-nutrients (Zn+Cu+B+Mo) with recommended dose reduced the sterility compared to NPKS as control. The trend in sterile spikelets panicle1 and grain yield was influenced by micro-nutrients. Addition of micro-nutrients showed an improvement in grain yield of rice compared to the control and significantly higher grain yields were achieved in treatments with application of all micro-nutrients (Zn+Cu+B+Mo) followed subsequently by Zn+Cu+B and Cu+B+Mo with yield increments of 24.22, 20.07 and 18.69% compared to the control. In a study with number of seedlings hill' and 20 cm deep irrigation showed that two seedlings hill1 performed the best compared to other treatments. Deep irrigation applied at 45 and 60 DAT reduced the production of late tillers and achieved higher yield. Higher or lower doses of micro-nutrients against the recommended ones did not reduce the grain sterility under low temperature condition. A study with micro- nutrient, transplanting date and package of agronomic practices revealed that the application of Zn+Cu+B+Mo along with major fertilizing elements in recommended doses reduced sterility by 5.66% and increased grain yield by 16.05% over control and late December transplanting performed best among transplanting dates. The agronomic package comprising 50-day old seedling + 20cmx15cm spacing was found superior in respect of reducing sterility and increasing yield to other packages.