چكيده لاتين :
Introduction Weed control is an essential part of all crop production systems. Weeds reduce yields by competing with crops for water, nutrients, and sunlight. Weeds also directly reduce profits by hindering harvest operations, lowering crop quality, and producing chemicals which are harmful to crop plants. Results of researches have shown that good weed control within the first four to six weeks after crops are planted is critical in order to avoid a yield reduction by weeds. There are many cultural, mechanical, and chemical methods of weed control which are extremely effective if applied at the correct time. Fields that are kept free of weeds for the first four to six weeks after planting give the crop a "head start " which enables it to shade out or otherwise out compete weeds that emerge later in the season.
Materials and Methods In order to study the effect of weeds interference on morphological traits, yield and yield components of three safflower cultivars, as well as weed species density and dry weight , a factorial experiment based on a randomized complete block design with three replications was conducted in factorial at the Agricultural and Natural Resources Center of South Khorasan province during 2012 growing season. Experimental treatments consisted of three safflower cultivars (Goldasht, Padideh and Golsefid) and six weed interferences (control or without weeds throughout the growing season, interference until stem elongation, branching, flowering, end of grain filling period and the end of growing season).. Measuring traits included the number of branches, head diameter, number of head per square meter, number of seed per head, seed weight, seed yield, biomass, oil percentage, and oil yield of safflower. Within weed species were identified, counted, clipped at ground level and oven-dried at 72 °C for 48 hours, then weighed to determine their dry matter. All data were subjected to analysis of variance using SAS statistical software and Duncan 's multiple range procedure was employed at probability level of 5%.
Results and Discussion Results showed that all measured traits except head diameter, weeds density and dry weight were significantly differed among cultivars. Number of head per square meter, seed and biological yield, oil percentage and oil yield in the Padideh cultivar was higher than two other cultivars whilst its seed yield had no significant difference with Golsefid cultivar. Interference treatments showed a significant effect on head diameter, number of seed per head, seed and biological yield, oil yield, weeds density and dry weight . Safflower seed yield decreased considerably by extending of weeds interference duration so that interference until flowering, end of grain filling period and the end of growing season were obtained 19.3%, 28.3% and 51.4% compared to control (296.37 g m-2), respectively. Also, weed interference until the end of growing season of safflower reduced oil yield in comparison to control by 35.6%. Simple correlation analysis, revealed seed yield was positively correlated with all the traits except seed weight and oil percentage. The highest weed density (98.7 plants per m2) was observed in interference until stem elongation. Also, increasing of interference duration caused decreased weed density per unit area., So that, weeds dry weight per unit area was increased until the end of grain filling stage, despite the decline in weed density. The results of our study demonstrated that extending of weed interference duration until the end of growing season led to reducing of safflower cultivars yield. Also, Padideh cultivar had the highest oil percentage and oil yield, 25.7%and 70.5 g m-2, respectively.
Conclusions The study of weed populations and their dry weight per unit area showed that weed dry weight has increased with increasing of weed interference period, in spite of decreasing of their density. The results revealed that the presence of weeds throughout the growing season reduces the yield of safflower cultivars while the level of decline was different in cultivars. Therefore, yield of Padideh cultivar in the presence and absence of weeds was more than two other cultivars. The highest seed yield was recorded from weed control treatments of early growth. In general, weed control in safflower should be done in branching or stem elongation stage.
