| This research investigated the symbiotic effectivity and competitiveness of three strains of Chinese fast-growers (Rhizobium fredii) in the greenhouse and in the field, and evaluated the competitive ability of siderophore over-producing mutants of Chinese fast-growers (developed through transposon-mediated mutation) in an alkaline soil of Iowa. In the greenhouse study on effectiveness, three Chinese fast-growers were tested along with two USDA slow-growers (Bradyrhizobium japonicum) on four soybean cultivars. There was a significant strain-by-cultivar interaction, and two of the fast-growers were as effective as USDA 123 in N fixation on most of the cultivars, but less effective than USDA 110 on all cultivars tested. In the competition studies, the competitiveness of the fast-growers was evaluated in the greenhouse against native bradyrhizobia in six different soils. Nodule occupancy by fast-growers ranged from 1.5 to 38.8%, and there were significant interactions among strains, soils, and cultivars. For field testing, two separate sites each year were selected in the summers of 1987 and 1988, and each of the three fast-growers was introduced into soil at approximately 10... |
