effect of row spacing and plant density on yield quality and quantity of soybean under weed competition

in order to study the effect of row spacing and plant density on quantity and quality yield of soybean in weed competitive condition, a field experiment was carried out at research farm of yasuj agricultural college in summer of 2011. experiment arrangement was split factorial base on randomized complete block design with three replication. the main factor included weed ( in two levels of control and non control of natural weed flora) and sub plots involved factorial of soybean row spacing ( whit three levels 30, 45 and 60 cm) and plant density (with three levels 40, 50 and 60 plants per square meter). results showed increased density and reduced row spacing increased soybean yield so that the maximum grain yield was obtained in 60 plants per square meter (2405 kg.ha-1) and 30 cm row spacing (2368 kg.ha-1). weed competition reduced by 37 percent soybean grain yield. increasing density and decreasing row space increased oil yield, whereas weed competition reduced by 38 percent oil yield. also with increased density and reduced soybean row spacing, weed dry weight was reduced, so that the minimum weight was obtained of row spacing of 30 cm (531/3g) and plant density of 60 plants m (523/2 g). the results indicating the effectiveness of the increase density and reducing row spacing of soybean for weed control.