INTERACTION BETWEEN A VESICULAR‐ARBUSCULAR MYCORRHIZA AND RHIZOBIUM AND THEIR EFFECTS ON SOYBEAN IN THE FIELD

Summary Interaction between Glomus fasciculatus and Rhizobium japonicum and their effects on soybean in the field was studied in a phosphorus deficient sandy loam soil with pH 5·6. The number, dry weight and nitrogen content of the root nodules in plants inoculated with Glomus plus Rhizobium were significantly more compared to plants inoculated with only Rhizobium. Rhizobium inoculation did not have any significant effect on sporulation of G. fasciculatus in the rhizosphere. Although soybean plants inoculated with G. fasciculatus recorded increased phosphorus content, dry weight and grain yield than uninoculated plants the differences were not statistically significant. In Rhizobium only inoculation markedly increased the nitrogen content of the plant and grain yield. Dual inoculation with both the symbionts increased significantly the dry weight of the shoot and its nitrogen content over single inoculation with either Glomus or Rhizobium. These results suggest that vesicular–arbuscular (VA) mycorrhiza can greatly assist nodulation and nitrogen fixation in field growth soybean inoculated with rhizobia.