Using Plant Volume to Quantify Interference in Corn (Zea mays) Neighborhoods

Measurements of above-ground plant volume were used to quantify corn interference with common cocklebur and velvetleaf. Separate experiments were carried out for each weed species in which neighborhoods with a radius of 50 cm were established around target plants of both species, selected from a range of corn plus cocklebur or velvetleaf densities. Height and canopy area of target plants and neighbor corn and weed populations were measured periodically during the growing season. Target plant (corn, cocklebur, or velvetleaf) size as well as corn and weed population size within each neighborhood were quantified as cylindrical volumes. Regression analysis was used to quantify the relationship between target plant seed production and cylindrical volumes of the target and neighbor species. Both target and neighbor plant volumes were correlated with target plant seed production for all species. The ratio of target plant volume to total neighborhood plant volume (volume ratio) was the independent variable that accounted for the most variation in target plant seed production. These volume-based variables may be used to develop competitive indices in physico-empirical based interference models.