Abstract
Nine experiments were conducted at the Agronomy Field Laboratory of Bangladesh Agricultural University, Mymensingh for consecutive three years from 1999 with a view to improving the productivity of T. aman rice-mustard cropping sequence. The study included selection of high yielding and short duration varieties of rice, and high yielding and late varieties of mustard for the purpose along with inclusion of several agronomic practices to influence the productivity of the cropping sequence. The results over three seasons revealed that the T. aman rice varieties CNSGC-6, BRRIdhan33, BR3, BR14, BRRIdhan32 and BINAshail appeared as early maturing but BINAshail was not good grain yielder. From the last two years trial, a package of agronomic practices for T. aman rice with 55 kg N ha+ 30 kg P ha+ 45-day old seedlings transplanted on 10-20 July was found effective to curtail the field duration of T. aman rice by 7-8 days compared to that achieved from the normal practices. This accommodated mustard sowing in the same land following the harvest of T. aman rice as early as 10 November. On the other hand, trials with mustard in the free land showed that late sowing up to 01 December as against 07 November sowing consistently reduced the seed yield for all varieties but the reduction was minimum (16.04-23.85%) with Shambal, RS-81 and Rai-5. Yield reductions due to late sowings were severe (ranging from 49.41-71.84%) for mustard varieties Tori-7, Sampad, TS-72, SS-75, BARIsharisha-6, BARIsharisha-7, BARIsharisha-8, BINAsharisha-3 and BINAsharisha-4. However, the seed yield (1.05 t ha1) of BARIsharisha-7 was found to be acceptable as observed from the last sowing date (01 December). Therefore, this confirmed that the mustard varieties. Shambal, RS-81, Rai-5 and BARIsharisha-7 were found suitable for late sowing. Further, a package of agronomic practices for mustard consisting of a higher rate nitrogen of 210 kg N ha1, a narrow row spacing of 20 cm and a higher population of 90 plants m' was found effective as it gave 29.21% higher seed yield of late sown mustard in comparison to the control treatment receiving 140 kg N ha+ 30 cm row spacing + 60 plants m2. BARIsharisha-7 was the best mustard variety to follow after harvest of T. aman rice varieties CNSGC-6, BRRIdhan33, BR3, BRRIdhan32 and BR14 along with the selected agronomic package of practices for mustard to boost the yield further. Considering the rice equivalent yields (REY) of the T. aman rice-mustard cropping sequences, CNSGC-6-BARIsharisha-7, BRRIdhan33-BARIsharisha-7, BR3- BARIsharisha-7, BRRIdhan32-BARIsharisha-7, BR14-BARIsharisha-7 and BRRIdhan33- Shambal were found as the productive sequences having REY values of 9.05, 8.00, 7.09, 7.43, 7.03 and 6.58 t ha', respectively and use of favourable agronomic package of practices both in T. aman rice and mustard further improved these cropping sequences in terms of productivity (REY values of 9.05, 8.13, 7.58, 8.09, 7.12 and 6.58 t ha", respectively). An economic analysis of the data revealed that the T. aman rice-mustard cropping sequences with economically viable BCR values (>1.50) were: (i) CNSGC-6-BARIsharisha-7 (1.85), (ii) BRRIdhan33- BARIsharisha-7 (1.62), (iii) BRRIdhan32-BARIsharisha-7 (1.64) and (iv) BR3-BARIsharisha-7 (1.51) with rice seedlings transplanted on 10-20 July receiving favourable agronomic package of practices, and these ultimately allowed mustard sowing profitable up to 18 November.