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Field study was conducted to evaluate redroot pigweed interference with soybean. The experiment was established as a factorial in a randomized complete block design with three replications. In this experiment different times of emergence (Ve: redroot pigweed planted simultaneously with soybean, Vc: redroot pigweed planted at the cotyledon leaf stage of soybean, V2: redroot pigweed planted at the second trifoliate leaf stage of soybean) and densities of redroot pigweed (10, 20 and 40 plants/m-1) were studied. Yield and yield components of soybean at different times of emergence and densities of redroot pigweed were significant. Soybean yield was reduced by 44.75% and 39.21% when redroot pigweed did emerge at the same time with soybean, and at a density of40 plants / m-1, respectively. When redroot pigweed emerged at the third trifoliate leaf stage of soybean, neither yield nor yield components was effected by redroot pigweed densities.