744 PRINCIPLES OF SOIL MICROBIOLOGY 



volatile antiseptics) increased the rate of oxidation in the soil, as well 

 as the numbers of bacteria. Similar observations for bacterial num- 

 bers were made previously (1901) by Hiltner and Stormer 17 who treated 

 the soil with CS 2 . Russell and Hutchinson also found that the high 

 numbers in partially sterilized soil rose for a time even higher if a 

 little fresh untreated soil was added to the partially sterilized soil; 

 later, however, the numbers in the soil reinoculated with fresh soil 

 fell. 



Partial sterilization of soil can be accomplished by heating the soil 

 or by treating it with various antiseptics. By the use of heat (steam 

 or dry heat) the soil can be partially or completely sterilized, depending 

 on the temperature and length of treatment. To sterilize the soil 

 completely, it must be subjected to steam pressure for two hours at 

 15 pounds, or for one hour, on seven consecutive days, in flowing 

 steam. Temperatures less than 100°C. only destroy certain groups of 

 microorganisms; at 60° to 65°, for example, living protozoa, particularly 

 the large forms, and fungus mycelium and spores, 18 as well as vegetative 

 cells of various bacteria are destroyed. To partially sterilize a soil is to 

 treat it in such a manner as to destroy certain groups of organisms and 

 leave others uninjured. Soil partially or completely sterilized by heat 

 becomes a favorable medium for the growth of certain groups of fungi 

 and bacteria. 



A large number of antiseptics bring about true partial sterilization 

 with the following results: 19,20 



o. An initial decrease in the number of bacteria followed by a large sustained 

 rise. 



b. The destruction of the protozoa and nitrifying organisms. 



c. An initial increase of ammonia followed by a considerable increase in the 

 rate of ammonia formation and consequently of soil productivity. 



d. No increase in the dose of the antiseptic causes any change in the results 

 obtained, once true partial sterilization has set in. 



e. The complete or almost complete destruction of the soil fungi, 21 of soil 

 nematodes and other soil infesting worms and insects. 22 



17 Hiltner and Stormer, 1903 (p. 12). 



18 Thorn and Ayers, Jour. Agr. Res., 6: 153-166. 1916. 



19 Buddin, W. Partial sterilization of soil by volatile and non-volatile antisep- 

 tics. Jour. Agr. Sci., 6: 417-451. 1914. 



20 Russell, E. J. The recent work at Rothamsted on the partial sterilization 

 of soil. Intern. Inst. Agr., Bur. Agr. Int. PI. Dis., 8. 1917, No. 5. 



21 Waksman and Starkey, 1923 (p. 739). 



22 Russell, E. J. The partial sterilization of soils. Jour. Roy. Hort. Soc, 

 56: 236-246. 1920. 



