Effect of drought stress and strains of Bradyrhizobium japonicum on grain yield and associated characteristics in soybean (cv. Clark) in Borujerd

In order to evaluate grain yield and associated characteristics in soybean (cv. Clark) under the conditions of drought stress and Bradyrhizobium japonicum strains, an experiment was carridout in 2003 & 2004 cropping seasons, using split plot arrangements based on randomized complete block design with three replications in Agriculture Research Statioin of Borujerd, Iran. Irrigation levels were assigned to the main plots (four levels); full irrigation, mild stress (85% plant water requirement), moderate stress (70% plant water requirement), severe stress (55% plant water requirement). Sub-plots were Bradyrhizobium japonicum strains (four levels); control, Helinitro, Rizoking, Nitragin. The amount of irrigation water was calculated using plant water requirement and the atmometer. At planting seeds were inoculated with bacterium strains. Biological yield, grain yield, harvest index and hundred grain weight was measured and determined. Results indicated that grain yield was different under stress and full irrigation conditions. In full irrigation condition maximum grain yield (458 g.m-2) and biological yield (870 g.m-2) were produced by Nitragin strain. Under stress conditions, the efficiency of strains was not different under mild and moderate stresses. Higher grain and biological yield obtained by Rizoking strain. Therefore, this strain had better adaptation to modrate drought stress condition, however in severe drought stress no difference among bacterium strains was observed.