828 PRINCIPLES OF SOIL MICROBIOLOGY 



yield of soybeans 1787 pounds per acre, or more than threefold; it also 

 resulted in a net gain of nitrogen of 57 pounds per acre, 87 per cent of 

 which was in the tops. The residue left after the crop has been removed, 

 also benefits the succeeding crop. An average increase in the total 

 nitrogen content of the crop, as a result of inoculation, is given as 122 

 pounds per acre for American soil, and 200 pounds per acre for German 

 soil. 



Inoculation of non-leguminous plants with nodule bacteria. Various 

 attempts have been made to inoculate nodule bacteria upon non-legu- 

 minous plants, with variable success. Burrill and Hansen, 37 basing 

 their conclusions on their own observations and reports of other inves- 

 tigators, reported the results to be absolutely negative. Blunck, 38 

 however, reported positive results. He grew the organisms first on a 

 synthetic medium, then added to the medium an extract of the roots of 

 the non-leguminous plant, then grew the organism on the sterile dead 

 root of the plant, and finally on the living root. By this process of 

 gradual adaptation, Blunck claims to have obtained positive results. 

 However, in view of the fact that these results have not yet been con- 

 firmed, nor has Blunck himself brought further evidence to substantiate 

 his hypothesis, we must consider the results as doubtful. Various other 

 claims to discoveries of cultures of symbiotic nitrogen-fixing bacteria 

 adapted to non-leguminous plants are usually found to be worthless on 

 careful study. As far as our present information is concerned, non- 

 legumes cannot yet be inoculated with beneficial results. 39 



Inoculation of soil with non-symbiotic nitrogen fixing bacteria. It has 

 long been known that a soil is capable of moderating in some way the 

 losses of nitrogen due to removal in crop, drainage, etc. From various 

 practical observations, it has been established that one hectare of soil 

 of Central Europe is capable of fixing between 10 to 60 kilograms of 

 nitrogen per year, independent of the leguminous plants. 40 The most 

 abundant and most active of the non-symbiotic nitrogen fixing organ- 

 isms are the species of Azotobacter and Bac. amylobacter. As pointed 

 out elsewhere, the most important factors influencing the activity of 



37 Burrill and Hansen, 1917 (p. 126). 



38 Blunck, G. Die Anpassung der Knollchenbakterien an Nichtleguminosen. 

 Centrbl. Bakt. II, 51: 87-90. 1920. 



39 Kordes, H. Kritische Besprechung der Frage "Impfung der Nichtlegu- 

 minosen." Ztschr. Pflanzenenahr. u. Dung., 4B: 382-394. 1925. 



40 Omeliansky, V. L. On the application of non-symbiotic nitrogen-fixing 

 bacteria for soil fertilization. Russian Jour. Microb., 2: 125-139. 1915. 



