Yield and Yield Components Response of Corn/Soybean Intercrop to Simultaneous Competition of Redroot Pigweed and Jimson weed

In order to investigate the role of intercropping of corn/soybean on the resource use efficiency and suppression of weeds, a field experiment was carried out at the Faculty of Agriculture Research Farm, University of Tehran in 2006. Treatments were arranged in a factorial experiment based on a randomized complete block design with three replications. Treatments were five different mixing ratios of corn (Zea mays) and soybean (Glycine max) consisting of 100%: 0% (P1), 75%: 25% (P2), 50%: 50% (P3), 25%: 75% (P4) and 0%: 100% (P5). The weed infestation consisted of one weed free (W1), and three levels of weed infestation of redroot pigweed (Amaranthus retroflexus) (W2), jimson weed (Datura stramonium) (W3) and a simultaneous presence of redroot pigweed and jimson weed (W4). Weed density for both species was 15 plant m-1 of crop row in weed infested treatments. The Correspondence to: M. Aghaalikhani, maghaalikhani@modares.ac.ir results showed the highest yield of corn (9627.8 kg ha-1) was obtained in the P2W1 treatment, and the lowest (3916.7 kg ha-1) was in P2W4. But the highest yield of soybean (5050.00 kg ha-1) was seen in P5W1 and the lowest (365.67 kg ha-1) in P2W4. Some yield components of corn such as the kernel row number per ear, kernel number per row, and 1000 kernel weight were highest for P4W1, but the harvest Index was highest (0.45) for P2W1 and lowest (0.20) for P4W4. Some yield components of soybean such as pod number per plant, grain number per pod and 1000 grain weight were highest in the monoculture of soybean and the weed free treatment (P5W1). This treatment had the highest soybean harvest index. It could be concluded that decreasing the corn/soybean ratio in the cropping rows will increase the corn and soybean yield components. The highest weed biomass (376.73 g m-2) was obtained in the monoculture of soybean infested with jimson weed and redroot pigweed. Therefore, it could be stated that corn/soybean intercropping significantly reduced the weed biomass comparing to both monocultures.