Evaluation of competitive ability in two sesame (Sesamum indicum L.) cultivars with cocklebur (Xanthium strumarium L.) in different crop row spacing

In order to investigate the effect of crop row spacing and cocklebur (Xanthium strumarium) densities on height, leaf area index and total dry matter of two sesame cultivars, a Field experiment was conducted in 2009-2010 growing season at Research Farm of University of Agricultural Sciences and Natural Resources of Gorgan, Iran. The experiment was established as factorial arrangement using a randomized complete block design with three replications. The factors included different densities of cocklebur (0, 2, 4, 6 and 8 plant m-2) and two cultivars of sesame (Oltan, Yekta) and three sesame row spacings (35, 45 and 55 cm). The results showed significant effect of cocklebur density and sesame cultivar on height of crop but the effect of row spacing was not significant. Under competition Oltan had more LAI and biomass in comparison with Yekta cultivar. Based on the results leaf area distribution in the canopy, leaf area of sesame in each layer redused with increasing the cocklebur density in all sesame row spacings. Distribution of leaf in sesame is symmetrical parabolic shape and the maximum leaf area was located in the middle layer, but leaf area distribution in the canopy of cocklebur was asymmetric and the most LAI was distributed in the upper layers of canopy resulting in advantage of the weed in competition with sesame.