CHENOPODIUM ALBUM L. ناشي از تداخل سلمه تره ZEAMAYSL ارزيابي مدلهاي تجربي رقابت مبتني بر تراكم ، زمان سنجي سبزشدن و سطح برگ نسبي علف هرز، در شبيه سازي كاهش عملكرد ذرت

Evaluation of empirical models based upon weed density, time of emergence and relative leaf area to predict corn (Zea mays L.) yield loss caused by common lambsquarters (Chenopodium album L.) interference

The performances of four empirical models of weed-crop competition were evaluated to simulate corn (Zea mays L.) yield losses caused by interference from common lambsquarters (Chenopodium album L.) in 2001 in Karaj. The experiment was conducted in a complete randomized block design with three replications. Treatments were chosen to provide five different weed densities (0, 2, 5, 10 and 15 plants m-ʹ) and three times of weed emergence (VE, V2-V3 and V4-V5 of corn growth stage). Results showed time of weed emergence was more important than weed density, when describing the impact of common lambsquarters on corn yield. Therefore, the model based upon weed density couldnʹt simulate reduction in crop yield due to weed competition accurately. (R2=0.38, RMS=469.8). Although the potential and ability of this model was rejected, this model had an acceptable performance in each time of weed emergence. Parameter estimates of this model showed the relationship between weed density and crop yield loss had a tendency from rectangular hyperbola into linear, with delay in weed emergence. The model incorporating common lambsquarters density and time of emergence gave a better description of corn yield loss (R2=0.88, RMS=91.3). This model showed that common lambsquarters emergence after V8 of corn growth stage (45 DAE), couldnʹt reduce corn yield. Relationship between corn yield loss and common lambsquarters competition was best described by the two-parameter model of relative leaf area (R2= 0.91, RMS=0.006). The relative damage coefficient (q) of this model showed that common lambsquarters was more competitive than corn (q=1.81).