Effect of pre-emergence herbicides on weed control, seed yield and returns of soybean (Glycine max)

An experiment on chemical weed control in soybean was conducted during kharif 2008 to evaluate the efficiency of different herbicides. Two hand weedings at 15 and 35 days after sowing (DAS), and among herbicidal treatments, application of metribuzin both @ 650 g a. i./ha and at a lower dose of 500 g a. i./ha were found effective in reducing weed density and weed dry matter at 30 and 60 DAS, resulting in higher weed control efficiency over other herbicides. With the highest seed yield of 1636 kg/ha and haulm yield of 2358 kg/ha hand weeding at 15 and 35 DAS was found superior to all other chemical weed control treatments except the application of metribuzin @ 650 g a. i./ha which recorded a seed yield of 1523 kg/ha and weed index value of 6.9%. This was found at a par with same herbicide applied at a lower dose of 500 g a. i./ha (1415 kg/ha). The highest gross returns and net returns were obtained with hand weeding at 15 and 35 DAS, but benefit : cost ratio was highest with metribuzin @ 650 g a. i./ha as pre-emergence (2.27) followed by same herbicide @ 500 g a. i./ha as pre-emergence applications (2.15).