Winogradsky in 1925 developed the spontaneous culture method for studying the occurrence and activities of the aerobic non-symbiotic nitrogen fixing organisms in the soil. Using this method in conjunction with the silica gel method he was able to determine the nitrogen fixing power of the soil and the relative number of soil micro-organisms which will grow on the surface of the spontaneous culture plates. These organisms Winogradsky believed represented the aerobic non-symbiotic nitrogen fixing organisms of the soil and members of the Azotobacter genus were very prevalent in the colonies which developed.
Proceedings of the Iowa Academy of Science
©1931 Iowa Academy of Science, Inc.
Young, Arthur W. and Walker, R. H.
"Experiments with the Winogradsky Spontaneous Culture Test on Iowa Soils,"
Proceedings of the Iowa Academy of Science, 38(1), 313-320.
Available at: https://scholarworks.uni.edu/pias/vol38/iss1/110