Effect of Nitrogen and Weed Management on Direct-Wet Seeded and Transplanted Aman and Boro Rice

The experiments were carried out at the farm of Bangladesh Rice Research Institute, Gazipur during 2000-2002 to find out the effect of N and weed management practices on the growth and yield of direct seeded Aman and Boro rice compared to transplanted method and their economic profitability. The treatments were assigned in a split-plot design with planting methods in the main plot and combination of N and weed management in the sub-plot. The results indicated that there was herbicide toxicity, which was recovered after 21 days of herbicide application. Although higher tiller number was observed with broadcast (BC) at vegetative stage, the difference was insignificant for panicle production. Significantly higher dry matter (DM) production was found in transplanting (TP) than BC, especially in Boro season. Similar pattern followed for crop growth rate (CGR) and leaf area index (LAI). In most cases, 2 hand weeding (HW) and Ronstar + 1 HW helped in producing more number of tillers than Ronstar alone in Boro season. The BC and TP methods gave similar grain yields. There was no such variation in grain yield due to N management, although 4 to 7% higher grain yield was recorded with LCC based N management than 3 splits with or without basal N application. About 12% N could be saved with LCC based N management in Aman season without decreasing grain yield. Weed density and weed dry weight were higher in Boro than in Aman season. Nitrogen application and its management did not affect weed DM production in most cases. TP method had significantly higher N uptake than BC in Boro season. Significantly higher N uptake was found in 2HW and Ronstar + 1 HW compared to Ronstar alone. Crop establishment methods did not significantly influence the various indices of N utilization efficiency both in Boro and Aman seasons. In BC method, there was significantly higher N uptake by weeds than in TP method in different seasons. Effects of interaction of different parameters like tiller number, DM, CGR and LAI were significant. Production cost was higher in TP method than in BC method. The gross margin was higher in TP than in direct-seeded rice. The benefit cost ratio (BCR) of BC method was higher compared to other planting methods. The LCC based N management alongwith weed control by Ronstar alone or Ronstar + 1 HW had higher BCR in both the seasons. The basal N plus LCC based N management alongwith weed control by Ronstar supplemented with 1 HW would increase grain yield of direct-wet seeded rice.