الفهرس 
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Abstract
Objectives: Isolation of different nitrogen fixers, phosphate solubilizers and potassium releasers from rhizosphere of some plants, efficiency evaluation of these isolates for nitrogen fixation, phosphate solubilization, potassium releasing and production of phytohormones, studying the effect of inoculation with most efficient bacterial isolates individually and/or in a mixture on the growth and yield of wheat and/or onion crops which are considered as from the most economical crops in Egypt. Moreover studying the effect of bio-fertilization on the microbial changes in the rhizosphere of wheat and onion plants. Methods & Results: •Fifteen isolates of Azotobacter spp. were isolated, the most active isolate was No. AZ 8 and identified as Azotobacter chroococcum MF135558 , twenty-one phosphate-solubilizing bacteria (PSB) were isolated, the most active isolate was PSB 14 and identified as Klebsiella oxytoca MF135559 and five isolates of K-releasing bacteria (KRB) were isolated on Alexandroov’s medium, the most efficient isolate namely KRB-2 and identified as Rhizobium pusense MF135560. •The previously three bacterial isolates (AZ-8, PSB-14 and KRB-2) have the ability to produce indole acetic acid (IAA) actively. Seven local strains and one isolate of cyanobacteria were tested for their ability to fix the atmospheric nitrogen. The most active cyanobacterial strains were N. muscorum, A. fertilisima II, A. Variabilis II and A. oryzae. A field experiment was carried out on the farm of faculty of Agriculture, Mansoura University, Mansoura, Egypt during the winter season of 2016 to study the effect of bio-fertilizationon the growth and yield of wheat and onion plants. In wheat experiment, the treatment T 9 (Az. chroococcum + K. oxytoca + 75 % dose of N) gave the highest value of grain and straw yield with an increase by 21.87% and 19.01%, respectively over the control treatment. On the other hand, in onion experiment the treatment T4 (Az. chroococcum + 75 % dose of NK) gave the highest total yield with an increase by 6.19% over the control treatment. Also, the bio-fertilization has a pronounced increase in microbial count in comparison with the mineral fertilization. The following study recommend by the possibility of using Azotobacter chroococcum MF135558 in the presence of 75% dose of NK for enhancing growth and yield of onion plants and reduce chemical fertilizers usage. The bio-fertilization has a pronounced increase in microbial count in comparison with the mineral fertilization. Conclusion:from the current study, it could be recommend the possibility of using the dual bacterial inoculum, which containing Azotobacter chroococcum MF135558 and Klebsiella oxytoca MF135559 in the presence of 75% dose of N for enhancing growth and yield of wheat plants and the individual inoculum which containing Azotobacter chroococcum MF135558 in the presence of 75% dose of NK for enhancing growth and yield of onion plants.