Competitive effects of redroot pigweed (Amaranthus retroflexus) on the growth indices and yield of corn

The mutual effects of redroot pigweed ( Amaranthus retroflexus ) on corn ( Zea mays ) were evaluated in an experiment conducted in 2005 at the Iranian Plant Protection Research Institute at Qazvin, considering the different densities of redroot pigweed against four different corn densities. Redroot pigweed, at 0, 35, 50, 65, and 80 plants m⁻¹ row⁻¹, was arranged factorially with corn at four, five, six, and seven plants m⁻¹ row⁻¹ in a randomized complete block design. Crop–weed competition resulted in a reduction in the total dry matter, Leaf Area Index, and crop growth rate of corn. Furthermore, an increasing weed density ≤65 plants m⁻¹ row⁻¹ reduced the corn grain yield and biological yield. Overall, six corn plants m⁻¹ row⁻¹ was suggested as the optimum density of this crop in competition with redroot pigweed.