During the years which have elapsed since the discovery of the non-symbiotic nitrogen-fixing bacteria there have been extensive investigations on the characteristics and activities of this group of organisms. They have been found to be of great importance from the fertility standpoint, adding appreciable amounts of nitrogen to the soil annually where the conditions are favorable for their development. In many cases too, a correlation has been found between the ability of a soil to support a vigorous Azotobacter growth and its crop producing power.
Proceedings of the Iowa Academy of Science
©1929 Iowa Academy of Science, Inc.
Walker, R. H. and Sullivan, John L.
"The Spontaneous Culture Method for Studying the Non-Symbiotic Nitrogen Fixing Bacteria of the Soil,"
Proceedings of the Iowa Academy of Science, 36(1), 53-61.
Available at: https://scholarworks.uni.edu/pias/vol36/iss1/7