Improving the productivity and quality of black cumin (Nigella sativa) by using Azotobacter as N2 biofertilizer

Thirty one rhizosphere soil samples were collected from different gavernorates and localities cultivated with different standing crops. Samples were used for the isolation of N2-fixer Azotobacter sp. isolates. The purified isolates were identified as Azotobacter chroococcum. The purified isolates were tested for their N2 fixation activity, phosphates dissolving ability, production of plant growth promoting substances, exopolymer secretion, siderophores production, salicylic acid formation, and some enzymatic production. Out of these purified isolates namely Azo.4, Azo.5, Azo.9 and Azo.23 found to be more significant in the production of the aforementioned activities as compared with the other purified isolates. The four purified isolates were tested for some biochemical activities (hormonal activity and enzymes production) and used to prepare the effective microbial inoculants for black cumin (Nigella sativa) seeds. Results show that mixed inoculation with the four biofertilizer strains and using half dose of recommended N2-fertilizer enhanced the densities of the total microbial microflora, phosphate dissolving bacteria, azotobacters colonization, CO2 evolution in the rhizosphere of the inoculated plants and plant growth features in comparison with uninoculated plants (control). The effect of the crude oils of the produced black cumin seeds on some human pathogenic bacteria was studied. It was found that the crud fixed oil extracted from the seeds of plants has powerful antibacterial properties against this diverse genus of bacteria. However, the influence was different and depending on the tested bacterial strain.