IMPACT OF DUAL INOCULATION WITH Rhizobium sesbania AND VESICULAR-ARBUSCULAR MYCORRHIZA ON GROWTH AND NUTRITION OF Sesbania aegyptiaca IN A CALCAREOUS SOIL

A pot experiment was carried out to study the effect of inoculation with single and dual inoculants of symbiotic N₂-fixer R. sesbania and the vesicular-arbuscular (VA) mycorrhizal fungus Glomus macrocarpus on growth and nutrition of S. aegyptiaca in a calcareous soil amended with rock phosphate (0.5%) or fertilized with different levels of superphosphate.  A significant increase in fresh and dry weights of S. aegyptiaca was obtained after inoculation of plants particularly with dual inoculant, in the presence of ½ dose of superphosphate.  Incorporation of dual inoculants in the presence of ½ dose of P significantly increased the accumulation of N, P and K in S. aegyptiaca plants.  R. sesbania inoculant significantly increased the N content in S aegyptiaca plants in comparison with VA mycorhiza inoculated plants, while VA mycorrhiza inoculant significantly increased the P and K contents in plants compared with R. sesbania inoculated treatments.  Number and dry weights of nodules were increased in inoculated plants.  The maximum N₂-ase activity of S. aegyptiaca plants roots was recorded in 45 days old plants inoculated with dual inoculum particularly in the presence of low dose of superphosphate. The introduced biopreparations were able to colonize actively the rhizosphere of S. aegyptiaca plants in the presence of chemical fertilizer.  The maximum counts of total bacterial count in rhizosphere of 60 days old plants were found in the presence of dual inoculant and ½ dose of superphosphate.  High percentage of VA mycorrhiza colonization in S. aegyptiaca roots was recorded, indicating good ecological adaptation of the mycorrhizal fungus to the calcareous soil.  The high percentage of VA mycorrhiza colonization was found in inoculated and fertilized treatments.  The colonization was increased by elapsing of growth time.  The remarkable increase in VA mycorrhiza colonization was recorded in treatments inoculated with dual inoculum and fertilized with superphosphate.