Effectiveness of Pretilachlor and Pyrazosulfuron-Ethyl with the Application of Biochar against Weeds under Rainfed Aman Rice Relay Planted with Mustard

A field experiment at Sher-e-Bangla Agricultural University from July to December 2023 assessed the effectiveness of carbonaceous materials and herbicides on rainfed aman rice (Oryza sativa L. ssp. indica) and their effects on relay mustard (Brassica rapa L.). The study included treatments with no carbonaceous material (control), biochar (4 t ha^-1), and biochar compost (4 t ha^-1), along with herbicide combinations, including control and pyrazosulfuron-ethyl (150 g ha^-1), pretilachlor (1 L ha^-1), a mixture of pyrazosulfuron-ethyl (0.75%) and pretilachlor (30%) (2 kg ha^-1), and another mixture of pyrazosulfuron-ethyl (0.15%) and pretilachlor (6%) (2 kg ha^-1). The split-plot design included three replications and used BRRI dhan87 as a test rice variety. Mustard was seeded 15 days before rice harvest. The experimental field contained eight weed species from six families. The results showed significant effects at the 5% level on weed density, weed dry weight, plant height, chlorophyll content (SPAD), and yield-related parameters. The interaction of biochar compost with pyrazosulfuron-ethyl (0.75%) + pretilachlor (30%) consistently outperformed other treatments, recording the lowest weed density and dry weight, the highest plant height (130.21 cm), SPAD values, number of filled grains panicle^-1 (116.60), 1000-grain weight (24.33 g), and grain yield (5.50 t ha^-1). Similar results were noted with biochar compost interaction with pyrazosulfuron-ethyl (0.15%) + pretilachlor (6%). Residual effects on mustard emergence indicated potential inhibitory effects of pretilachlor with carbonaceous amendments. This study suggests that combining biochar compost and herbicides effectively controls weeds and improves rice yields in rainfed areas.