FUNCTIONAL-RELATIONSHIPS OF GROWTH AND COMPETITIVENESS IN PERENNIAL WEEDS AND COTTON (GOSSYPIUM-HIRSUTUM)

Growth characteristics and competitive relationships of cotton and three perennial weeds (johnsongrass, purple nutsedge, and yellow nutsedge) were investigated at the USDA Cotton Research Station in Shafter, CA. In growth analysis experiments, yellow nutsedge and johnsongrass had highest values for height, biomass, leaf area production, growth rate, and photosynthetic efficiency. The weeds exhibited greater, overall resource use and production efficiency than cotton, while cotton attained greater leafiness and canopy closure than weeds over the 10-wk experiment. Linear correlation indicated that most growth variables were significantly correlated with aggressivity (competitiveness); however, all correlation coefficients were less than 0.80. Stepwise multiple regression, using aggressivity as the dependent variable, defined 4 growth variables out of 12 that best described competitiveness. These were unit leaf rate (ULR), height, relative growth rate (RGR), and initial propagule weight (PWT). Thus, parameters of light utilization (ULR, height) and early establishment (RGR, PWT) were best predictors of competitive success in this system.