Abstract
The growth and yield performance of hybrid and inbred rice varieties under different N management was studied. Field and net-house experiments were conducted during June 2001 to July 2003 at Bangladesh Rice Research Institute (BRRI) farm under Boro (dry season) - T. aman (wet season) rice cropping pattern in medium low land conditions. In both the cases, the hybrid Sonarbangla-1 and BRRI hybrid dhanl and inbred varieties BRRI dhan31 and BRRI dhan29 were used. The main objective of the field experiments was to compare the growth and yield of hybrid and inbred varieties under different N management. The main objective of net-house experiment was to compare the root and shoot growth and yield performance of the varieties under controlled condition. The field experiment was laidout in randomized complete block design where factor A was the varieties and factor B was the N management. Zero to 160 kg N ha' with different application schedules, N application on the basis of SPAD value and urea supper granules (USG) @ 80 kg N ha1 were used as N management. The hybrid Sonarbangla-1 and BRRI hybrid dhanl were tested in both the T. aman (except 2001) and Boro seasons. The BRRI dhan31 and BRRI dhan29 were tested in T. aman and Boro season, respectively. The varieties Sonarbangla-1 and BRRI hybrid dhan performed better in terms of growth, yield and nitrogen use efficiency in Boro (dry) season compared to T. aman (wet) season. The grain yield of hybrids was 2.0-2.5 t ha in T. aman season. The same hybrids showed almost identical growth and yield as inbred varieties in Boro season. None of the hybrids out-yielded inbred BRRI dhan29. All varieties produced 5.0 t ha grain yield in Boro 2002 and 4.0-4.5 t ha in Boro 2003. The hybrid Sonarbangla-1 was found suitable in Boro season because of its shorter growth duration of only 140 days with higher productivity. Considering the N management, 120 kg N ha in 3 equal splits without basal (N4), SPAD-based N management (N7 and Ng) and urea supper granules (USG) @ 80 kg N ha' (N9) were found suitable for better growth, yield and N use efficiency of the tested rice varieties in T. aman seasons. Basal N application and N application at flowering stage did not increase grain yield in T. aman season, even in the case of hybrids. On the other hand, 160 kg N ha1 in 4 equal splits with basal (Ns), SPAD-based N management (N, and Ng) and USG @ 80 kg N ha' (N9) were found suitable for better growth, yield and N use efficiency in Boro season. The N use efficiency was 20-25 % higher in crop demand based N management and USG compared to pre-scheduled N application. The variation in leaf color of the test varieties was very little. Sonarbangla-1 and BRRI hybrid dhan1 showed the critical LCC values of 3.5 in T. aman seasons but that varieties showed LCC values of 3.0 in Boro season. Inbred variety BRRI dhan31 showed critical LCC value of 3.5 in T. aman and BRRI dhan29 showed 3.0 in Boro season. A positive and strong linear relationship was observed between flag leaf chlorophyll content (mg g'') and the SPAD values (R2 = 0.82-0.94). Similar relationship was also observed between leaf N content (%) and SPAD value. Better growth performance at early growth stage of tested hybrids, did not reflect on the grain yield. The tested hybrid Sonarbangla-1 and BRRI hybrid dhan1 are not suitable for T. aman season. The LCC can be the substitute of SPAD meter in field level and farmers can avoid unnecessary urea application through assessing the leaf color.