Azotobacter

I believe, and this belief is based upon tentative facts, that the azotobacter are at the same time nitrifiers, i. e., that they possess a double function

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Investigations in this laboratory have shown that the presence or absence of Azotobacter in natural soils is very closely associated with, if not dependent upon, the absolute reaction of the soil solution

Source: wiktionary

It is therefore not surprising that azotobacters, introduced into soils of unwatered crops in semi-arid zones will die out rather rapidly.

Source: wiktionary

They are usually motile, oval or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime. Azotobacter is found in slightly acidic (A. beijerinckii) to neutral alkaline (A. chroococcum) soil.

Source: wiktionary