in order to evaluate the efficiency of empirical competition models for simulation of sugar beet (beta vulgaris l.) yield at interference with redroot pigweed (amaranthus retroflexus l.), a factorial experiment based on randomized complete block design with three replications was carried out. factors were weed densities (d1=1, d2= 4, d3= 8, d4=12 and d5=16 plants m-1 of row) and relative time o...