14H HATCH EXPERIMENT STATION. [Jan. 



A Comparison of the Numbers of Bacteria in Sterilized 



AND UnSTERILIZED SoILS. 

 BY A. VINCENT OSMUN. 



There has been repeated inquiry as to the effect steriliza- 

 tion of soil has upon its bacterial flora. In the absence of 

 any reliable experiments touching upon this question, it has 

 frequently been assumed that by soil sterilization the bac- 

 teria, and especially the beneficial ones, are destroyed, hence 

 injuring the soil. In regard to this question, it may be 

 stated that little is known al)out either the so-called bene- 

 ficial or injurious bacteria of greenhouse soils; and, in con- 

 sequence of a paucity of knowledge iqion this phase of the 

 subject, positive statements are out of place. From what is 

 already known about the effects of soil sterilization upon 

 plant growth and the changes which such soil undergoes, it 

 might be assumed upon a priori grounds that soil bacteria 

 Avould be found to exist more abundantly in sterilized soil 

 than in unsterilizcd soil. Moreover, it must be borne in 

 mind that absolute sterilization is never accom})li.shod, but 

 something more closely approaching pasteurization takes 

 place. All bacteria are by no means killed, as has been 

 shown by various tests made at this station. ^ Subjecting 

 soils to steam heat has a marked stimulating efi'ect on the 

 growth of plants. Observations at this station and experi- 

 ence of growers have shown this to l)e true. Just why 

 this treatment of soil should stimulate the growth of })lants 

 is not known. Sorauer^ suo-o-ests that steam heat makes the 

 humus compounds more available to })lants. It is not un- 

 likely that steam fiowing througli a soil also improves its 

 mechanical condition. 



The stimulating effect of soil sterilization on plant growth 

 suggested a similar effect on the bacterical content of soil so 

 treated ; and in order to obtain more evidence regarding 

 this point this ex})erinient was [)lanned : — 



Two boxes al)Out 20 inelies S(]uare and !• inches deep and 

 of c(iual weights were filled to the depth of about 5 inches 



* Hatch Experiment Station, Massacluisotts Report, 1!X)2, pp. 77, 7H. 



* Sorauer, The Physiology of Plants, pp. 45, 4(). 



