1. Alexander M 1961 Nitrogen Fixation Non-symbiotic inIntroduction to Soil Microbiology (New York: John Wiley) p. 311–316
2. Allen O N 1959Experiments in Soil Bacteriology (Minnesota: Burgess Pub. Co.) p. 5–9
3. Balasubramanian A, Shantaram M V, Sardeshpande J S and Rangaswami G 1972 Studies on certain microbiological properties of old permanent manurial plots;Madras Agric. J.
59 443–448
4. Cooper R 1959 Bacterial Fertilizers in Soviet Union;Soils and Fertil.
22 327–337
5. De P K 1952–1954 Annual Reports of Scheme for Research onAzotobacter, West Bengal