Responses of Corn to Plant Density and Weed Interference Period

3 Abstract: Studies have shown there are major advantages to increasing crop density in integrated weed management programs. Research was conducted in Zanjan University research fields to evaluate the effect of weed interference period and crop density on corn yield and yield components (Rows per ear, Kernels per ear and 1000-grain weight). The experimental design was a randomized complete block design with a factorial arrangement replicated three times. The treatments were six periods of weed interference (0, 48, 62, 76, 90, 120 d after sowing) and two crop densities (7, 9 plants m ). Results showed that crop density 2 had a significant effect on kernels per ear and grain yield (p < 0.01). Mean comparisons showed that increasing crop density increased grain yield from 7107.5 to 8511.5 kg ha and this factor decreased the number of 1 Kernels per ear significantly. Increasing weed interference period decreased grain yield and yield components. The highest grain yield was recorded for the whole-season weed-free treatment; the lowest grain yield was found for the whole-season weed-infested treatment. The effect of weed interference period on corn grain yield was higher at low than at high corn density. Yield of the corn was reduced more by low plant density and weed interference period than high corn density. The critical time of weed removal ranged from 21 to 19 day after planting for 7 and 9 plants m respectively to prevent yield losses of 5%. Consequently, selection of corn 2 density and a suitable time for removing weeds should be an integral part in the design of a weed management system.