Fertilizer nitrogen rate and the response of weeds to herbicides

Abstract Differences in plant community composition have been attributed to abiotic field characteristics, crop type, localized predation, farm implement traffic, and natural dispersal mechanisms. Nitrogen (N) fertilizer rates and herbicides also are known to influence weed community structure, although their interaction has not been reported in the literature. A growth room experiment was conducted using three weed species (green foxtail, redroot pigweed, and velvetleaf) and five herbicides (nicosulfuron, atrazine, glufosinate, glyphosate, and mesotrione) differing in their mode of action and efficacy to the selected species. The experiment was conducted in growth chambers with two levels of N fertilization (low: 0.7 mM N and high: 7.7 mM N). Weeds were grown to the two- to five-leaf stage (depending on species), treated with the appropriate herbicide, and harvested approximately 2 wk after treatment. The herbicide dose at which a 50% reduction in biomass occurred (GR50) was determined using log-logistic...