Abstract
Nine species of cyanobacteria were isolated from agricultural soil of Western region in the Kingdom of Saudi Arabia. Except for Phormidium sp, and Oscillatoria sp., all the isolated species were able to fix atmospheric nitrogen. The seven nitrogen fixing species exhibited different potentialities for atmospheric nitrogen fixation. The descending order for their potencies was as follows: Anabaena cylindrica; Anabaena sp.; Gloeocapsa sp.; Synechococcus sp.; Chroococcus sp.; Lyngbya sp.; Nostoc commune.
It was also found that there was a correlation between the efficiencies of cyanobacteria species for atmospheric nitrogen fixation and their biological activities.
Results obtained revealed the biomass of some cyanobacteria species to have stimulatory effect on the rate of respiration of cyanobacteria and other soil microbes, while the biomass of other cyanobacteria species had inhibitory effect.
Upon tl:sting efficiency of these atmospheric nitrogen fixers in fulfilling the requirements of wheat plant for nitrogen, in the absence of this element in the growth medium, it was found that Nostoc commune :and Anabaena cylindrica could supply wheat plant with atmospheric nitrogen to maintain its vegetative growth. Therefore, these species: of cyanobacteria could be used as biofertilizers instead of utilizing expensive industrial chemical manures.