Interactions between maize-weed competition and herbicide dose: relationships among the components of Xanthium strumarium, Amaranthus retrolexus and Zea maize under herbicide dose

A two-year field experiment was conducted in 2007 and 2008 to determine the relationship between competitive indices of maize, Xanthium strumarium and Amaranthus retrolexus. Five doses of herbicide nicosulfuron as the main factor, and a combination of 16 densities comprised four densities of A. retroflexus × four densities of X. strumarium as sub plots were arranged in a one-replicate split factorial. Four indices were considered for maize which is influenced by competition: grain yield, biomass, leaf area, and plant height. Biomass was determined as the direct factor that controlled grain yield, and the biomass was directly depended on maize leaf area. The plant height had the most important role in the maize leaf area. Field observations confirmed the efficacy of plant height in evaluating the plant competition. Increase in X. strumarium biomass indicated direct effect on maize grain yield. The X. strumarium biomass was controlled by its leaf area and the number of lateral shoots. However, the plant density as an external factor had significant effect on crop-weeds competition, herbicide dose was determined the most important determinant that caused major change in the X. strumarium height and leaf area. Among the A. retroflexus indices, its leaf area was the most effective, which was directly controlled by its biomass. Deep understanding of the system behavior, relations and interactions with herbicide is a great help in managing the weed damage.