Inoculation efficiency of rice plants with proper species of Azolla was studied. In this research two species of Azolla namely Azolla filiculoides and A. pinnata were tested for growth efficiency and nitrogen fixation rate. Re¬sults showed that Azolla filiculoides gave greater fresh and dry yield of bio¬mass compared with A. pinnata. Also, A. filiculoides gave higher percentage of total nitrogen and N2-ase activity than A. pinnata. So, A. filiculoides was used in further study. When rice plants were inoculated with Azolla as a bio¬fertilizer at a rate of 100 g and 150 g/m2 combined with 30 Kg P205/fed, the highest densities of total bacteria and inorganic phosphate solubilizing bacte¬ria were obtained, respectively.
Counts of ammonifiers and nitrifiers were increased with the increasing of Azolla inoculum rate. Ammoniacal nitrogen was the highest with Azolla ap¬plication at a rate of 150 g/m2 combined with 45 kg P205/fed. Highest values of plant height, fresh and dry weights of shoot system were obtained from Azolla inoculum rate of 150 g/m2 combined with 30 kg P205/fed. Interaction effect between Azolla inoculum rates and P-levels was significant on total ni¬trogen, phosphorus and potassium in rice plants. Highest values of chlorophyll
a, b and carotenoids as well as total carbohydrates were obtained in the treat¬ment of Azolla inoculum at a rate of 150 g/m2 combined with 45 kg P205/fed. The highest values of grains and straw yield and 1000-grain weight of rice were obtained in the treatment of Azolla inoculation at a rate of 150 g/m2 combined with 30 kg P205/fed. in both seasons of cultivation.
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