832 PRINCIPLES OF SOIL MICROBIOLOGY 



from the commercial preparations rapidly succumb. The legume bacteria have 

 the opportunity of penetrating the roots of the leguminous plants, whereby they 

 are protected from competition with other bacteria. The protection is afforded 

 also when the leguminous plants are dead since the nodules do not decompose 

 so readily. 



2. Although soil bacteria fix appreciable quantities of nitrogen under laboratory 

 conditions and a definite success may be obtained on inoculating soil with such 

 bacteria, the use of rather expensive substances like mannite or sugar make it 

 rather prohibitive. The growth of algae was found to offer only questionable 

 hopes. 62 



Soil inoculation with autotrophic bacteria. A number of organisms 

 causing plant diseases can be affected in their growth by a proper 

 control of the soil reaction ; this is especially true of those that are very 

 sensitive to acidity, as in the case of diseases caused by actinomyces 

 (potato scab, etc.). The addition of sulfur to the soil is used as a means 

 of increasing the acidity of the soil to a point at which the development 

 of the disease-producing organism is checked. But before this can take 

 place, the sulfur has to be oxidized to sulfuric acid by proper bacteria. 

 All soils contain organisms capable of oxidizing elementary sulfur; 

 these may carry on the oxidation only very slowly, especially in certain 

 soils. When strong sulfur oxidizing organisms are added, the oxidation 

 of the sulfur may be hastened appreciably. This led to the development 

 of a commercial product, which consists of sulfur inoculated with a 

 crude culture of Thiobacillus thiooxidans. It still remains to be proved, 

 however, how long the culture will survive on the dry sulfur and how 

 efficient it may be, in comparison with the organisms present in ordinary 

 soils. 



The inoculation of soil with nitrifying bacteria, especially in case of 

 freshly drained swamps may also be of direct benefit. 



Inoculation of soil with heterotrophic, non-nitrogen-fixing microorgan- 

 isms. Attention has already been called to Caron's first attempt to 

 prepare a bacterial culture (alinit 53 ) for soil inoculation, with the idea of 

 stimulating the decomposition of organic matter in the soil. Although 



impfung mit freilebenden stickstoffsammelnden Bakterien. Fiihl. landw. Ztg., 

 69: 161-166. 1920; Centrbl. Bakt. II, 53: 409. 1921. 



62 Further information on the inoculation of soil with Azotobacter is given 

 by Emerson, P. Soil inoculation with Azotobacter. Iowa Agr. Exp. Sta. Res. 

 Bui. 45. 1918; Omeliansky, 1923 (p. 559); Brown, P. E., and Hart, W. J. Soil 

 inoculation with Azotobacter. Jour. Amer. Soc. Agr., 17: 456-473. 1925; Gainey, 

 P. L. Inoculating soil with Azotobacter. Soil Sci., 20: 73-86. 1925. 



13 Complete literature on alinit is given by Heinze, 1902 (p. 831). 



