EFFECT OF SALT STRESS ON SOME FREE LIVING NITROGEN FIXING BACTERIA IN THE SOIL (1)

The current investigation was carried out to evaluate the effect of salt stress in El- Forat Basin (Syria) on some free living nitrogen fixing bacteria in the soil. Soil samples were taken from different sites in saline soils: (3.34, 6.01, 9.48, 11.66, 15.31, 21.8, 50.8 and 126.7 dS/m). The obtained result, showed reduction in number of Total bacterial count, Fungi and nitrogen fixing bacteria under saline soil conditions. Started with 6.01 dS/ m. In addition, drastic effect on occurrence as number Azotobacter or clostridia in saline soils with 50.8 and 126.7 dS/m. However, pronounced persistence of Azospirillum was determined under the same condition. Bacterial isolates belonging to genus Azotobacter and Azospirillum were used in pot experiment to study the effect of different salt concentrations (sodium chloride) (0, 0.78, 2.3 4, 4.21, 6.25. and 9.37 dS/m) on the productivity of wheat plant inoculated with their isolates. The result showed that inoculation by Azotobacter and Azospirillum increased the total bacterial count, total nitrogen fixing bacteria and dehydrogenase activity as compared with uninoculated treatment, but clostridia counts was increased in the uninoculated soils under high salt concentrations. The isolates from Syrian soils showed adaptation in high salt concentrations and succeeded colonize the root plant. Therefore we could confirm successfully using of these isolates as Biofertilizers for saline soils to enhance plant productivity.