SOIL MICROBIOLOGICAL EQUILIBRIUM 763 



amoebae and bacteria being due more to the successive drying and 

 moistening of the test soil than to the action of amoebae on the bacteria. 



Various plant pathogenic fungi, particularly organisms like Fusarium, 

 Phytophthora, Melanospora, Rhizoctonia, Neocosmopora vasinfecta, 

 Cladosporium scabies, Sclerotinia, Synchytrium, spores of rusts and 

 smuts, are readily destroyed by volatile antiseptics, such as toluol, 

 carbon bisulfide, or by heat. 78 A soil containing over 100,000 fungi 

 (spores and pieces of mycelium) per gram becomes practically free 

 from fungi after treatment with steam or volatile antiseptics. Partial 

 sterilization of soil can thus correct the condition of soil sickness caused 

 by the development of certain specific plant pathogens. 79 



Hiltner 80 used a logical process of reasoning for demonstrating the 

 destruction of fungi and actinomyces by antiseptics. When straw is 

 applied to soil, the available nitrogen is stored away by the micro- 

 organisms to the detriment of higher plants. When the soil is treated 

 with carbon bisulfide, during or after the addition of straw, the in- 

 jurious influence is not observed. This is due to the fact that, with 

 straw fertilization, the soil nitrogen is stored away chiefly by fungi 

 and actinomyces. The disinfectant brings about an appreciable 

 reduction in the number of these organisms, thus leaving the soil 

 nitrogen available for higher plants. The favorable influence of CS 2 

 is due not merely to the destruction of the organisms directly injurious 

 to higher plants but also to the destruction of those which have a passive 

 effect by storing away the soil nitrogen. Parasitic nematodes, such 

 as Heterodera radicicola and various other worms, are also killed by 

 heating the soil to 60° to 90°C. or by volatile antiseptics like CS 2 . 



In view of the fact that actinomyces grow only very slowly and that 

 the injurious factor in the soil is apparently something which is slowly 

 growing, for an infection with 5 per cent of raw soil only begins to 

 show a limiting action upon the fortieth day, Greig-Smith suggested 

 that actinomyces are the limiting factor for bacterial activities. Not 

 all the disinfectants, however, injure the actinomyces alike. 



Interrelationships of microorganisms in the soil. If the soil could be 



78 Pathogenic fungi in soil and their treatment are described elsewhere; see 

 P. Waget. Sterilization et disinfection du sol. La Revue d. prod, chimiques., 

 22: 655. 1920; 4: 115. 1921; 6: 183. 1921. 



79 Kaserer, H. Versuche fiber Bodenmiidigkeit, besonders Leinmlidigkeit. 

 Mitt. Wien. Hochschule f. Bodenkultur., 2: 375-410. 1913-14; Russell, E. J., 

 and Petherbridge, F. R. Partial sterilization of soil for glasshouse work. Jour. 

 Board Agr., 19. 1913, No. 10. 



80 Hiltner, 1908 (p. 41). 



