Effect of Plant Density and Water Deficit on the Growth, Yield and Yield Component of Soybean (Glycine max (L.) Merrill)

In order to evaluate effect of plant density and water deficit on the growth, yield and yield component of soybean, an experiment was carried out in split plot design based on RCBD with four replications at the research station of Seed and Plant Improvement Institute in Karaj-Iran in 2006. In this experiment, water deficit treatment in three levels was placed as main plot (water withholding at reproductive stage until 50, 100 and 150 mm evaporation from evaporation pan in each irrigation period) and plant density in three levels as sub plot in (20, 30, 40 plant/m2). The results indicated that water deficit had significant effect on all studied traits and caused to reduce the plant height (23%), number of pod per plant (37%), number of grain per plant (48%), 1000-grain weight (14%) and grain yield (56%). Also in the water deficit condition, oil percentage was reduced and seed protein amount was increased. While plant density had not significant effect on the vegetative traits of plant and only had significant effect on some reproductive traits such as number of pod per plant (P < 0.05), pod weight and grain number per plant and grain yield (P < 0.05). Generally, the best treatment for obtaining the maximum yield and suitable vegetative and reproductive traits was water withholding until 50 mm evaporation from evaporation pan in each irrigation period and density of 20 plant/m2.