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 Yasouj Agricultural College in summer of 2011. Experiment arrangement was the factorial split-plot based on randomized complete block design with three replications. The main factor included weed (control and non control of natural weed flora) and sub plots involved factorial of soybean row spacing (with three levels 30, 45 and 60 cm) and plant density (with three levels 40, 50 and 60 plants.m-2). 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 up to 37 percent soybean grain yield. Increasing plant density and decreasing row space increased oil yield, whereas weed competition reduced up to 38 percent oil yield. In addition, with increased plant density and reduced soybean row spacing, weed dry weight was reduced, so that the minimum weed dry weight was obtained in 30 cm row spacing (531.3g.m-2) and 60 plants per m2 plant density (523.2 g.m-2). The results indicating the effectiveness of the increase plant density and reducing row spacing of soybean for weed control.