Modeling Herbicide Dose Effect and Common Cocklebur (Xanthium strumarium) Interference in Soybean (Glycin max)

Field experiment was conducted to study the interaction between imazethapeyr dose and Xanthium strumarium density on soybean yield. Four densities of weed (0, 4, 8 and 12 plant.m-2) × 5 doses of herbicide (0, 25, 50, 75 and 100 g a. i. ha-1) was assigned in a factorial arrange of treatments with four replications. A combined model incorporated standard dose response curve and rectangular hyperbola competition model gave a good description for soybean yield. When no herbicide was applied, soybean yield was decreased by 58, 73 and 80% at densities of 4, 8 and 12 plant.m-2. Where the densities of common cocklebur was low (0, 4 plant. m-2) applying herbicide at half of the recommended dose could save the yield by 90% however; with increasing weed densities to 8 and 12 plant.m-2, 20 and 30% yield loss was caused in soybean yield. No difference was found between herbicide application at 75 and 100 rate of the recommended dose.