Berthelot in 1888 was the first to suggest that nitrogen may be added to field soils through the activity of microorganisms. In 1901 Beijerinck isolated a non-symbiotic, aerobic, nitrogen-fixing organism which he called Azotobacter chroococcum. Since this time five other species belonging to this genus have been isolated and likewise have been found capable of fixing atmospheric nitrogen.
Proceedings of the Iowa Academy of Science
©1935 Iowa Academy of Science, Inc.
Martin, William P. and Walker, R. H.
"Preliminary Investigation of the Occurrence and Distribution of Azotobacter on the Soils in Iowa,"
Proceedings of the Iowa Academy of Science, 42(1), 55-61.
Available at: https://scholarworks.uni.edu/pias/vol42/iss1/10