Abstract
Rice production plays a vital role in the food security and livelihoods of the people of Bangladesh; however, the sustainability of puddled transplanted rice is threatened by increasing costs of production (labour and diesel) and declining groundwater levels in major rice producing areas. Replacement of puddling and transplanting with dry seeding of rice (DSR) into non-puddled soil has the potential to facilitate timely establishment and reducing establishment costs through reduced energy and labour for tillage and transplanting, becoming increasingly attractive to farmers in many parts of Asia. Dry seeding of boro and aman are not normally practised in Bangladesh and management strategies for DSR are not available. Therefore, a series of crop and weed management experiments on DSR were conducted on a clay loam soil at the RARS, BARI, Jessore, over three consecutive dry seasons (boro seasons of 2011-12, 2012-13, and 2013-14) and two wet seasons (aman seasons of 2012 and 2013). The studies mainly aimed to evaluate the effects of sowing date, cultivars, seed rate, nitrogen rate, and weed control methods in DSR systems. With these objectives, a total of six different experiments were conducted. Boro crops sown in early November emerged faster and had higher plant density than crops sown in late November, and also had better growth for the first couple of months after sowing. There was a consistent trend for highest grain yield (BRRI dha:128 4.7-5.0 t ha1 and BRRI dhan29 6.7-6.9 t ha1) with the 8 Nov sowing date, significantly higlier than yield of late November sowings, mainly due to lower floret numbers and lower fertility and more so for BRRI dhan29. The decline in floret fertility was associated with higher temperature during flowering. Cultivation of November-sown dry seeded boro is slightly risky given the complete failure of all crops in 2012-13 due to cold injury, and the severe low-temperature stress experienced by the later sowings in 2011-12. Wet soil as a result of untimely rainfall usually prevented sowing on the last two target dates (25 June and 5 July) in both years aman sowing, but not on the first two dates (25 May and 10 June). Rainfall analysis also suggested a high probability of being able to dry seed in late May/early June, and a low probability of being able to dry seed in late June/early July. For the late June/early July sowings, there was a strong positive relationship between plant density and yield, but this was not the case for earlier sowings. There were no consistent effects of seed rate on grain yield of the 25-May and 10-June sowings; however, for late June/carly July sowings, grain yield increased significantly as seed rate increased from 20 to 40 or 60 kg ha-1. Under weed-free conditions, higher crop yields were obtained at the seed rate of 40 kg ha-1 and thereafter, yield decreased slightly beyond 40 kg seed ha-1. Under partially-weedy conditions, yield increased by 30 to 33% with increases in seed rate from 20 to 100 kg ha-1 and it was due to decreases in weed biomass (by 41-60%). Maximum yield of all crops was achieved at the highest nitrogen (N) rate (180 and 160 kg ha-1 boro and aman, respectively) with seed rates of 40-60 kg ha-1. There was a strong linear relationship between N rate and total N uptake, and N uptake increased with increased in seed rate up to 60 kg ha-1 and declined as seed rate increased beyond this. Both agronomic (AEN) and recovery (REN) efficiency of N increased with increasing seed rate to 40 to 60 kg ha-1 and tended to decline at beyond this. The use of pre-emergence fb (followed by) post-emergence herbicide fb one hand weeding (HW) effectively controlled weeds for both of the crops and produced a similar yield with the weed-free treatment for all levels of N. However, weed management cost was also higher because of the involvement of one HW. Although the pre-emergence fb post-emergence treatment had always lower yield than the pre-emergence fb post-emergence fb one HW treatment but grain yield increased and net profit was similar when N rate increased from 120 to 160 kg ha-1. In the High Ganges River Floodplain and the Barind Tract of western and north western Bangladesh, changing from puddling and transplanting to dry seeding may be beneficial to farmers.