عنوان مقاله [English]
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 of weed emergence (i1=emerged with sugar beet; i2=10, i3= 20 and i4=30 days after sugar beet emergence) included with a weed free control plot. Yield data were analyzed by four nonlinear regression models. Results revealed that sugar beet LAI reduced, when weed density increased and redroot pigweed (RP) emerged earlier, and the role of weed density was more effective than time of emergence for this characteristic. In treatments with low sugar beet LAI, RP LAI was more. Full-season interference of 16 RP m-1 of row decreased sugar beet root yield from 75 tha-1 in control to 58 tha-1. Increasing of each weed plant, reduced sugar yield 1.3 and 0.3 tha-1 in density intervals of 8-12 and 12-16 plants m-1, respectively. Cousens model had the best sugar beet yield simulation based on RP density and relative emergence time because of high R-square, low standard error and low mean percentage error and root mean square error values. In this model, mean percentage error increased from 1.4% to 9.36% based on root yield and sugar yield, respectively.