1912.] PUBLIC DOCUMENT — No. 31. 121 



THE PRESENT STATUS OF SOIL 

 STERILIZATION. 



G. E. STONE. 



The term " soil sterilization '' has long been applied by com- 

 mercial growers to a system of heating soils, generally by the 

 nse of steam, to a temperature ranging from 180° to 212° F. 

 for the purpose of destroying certain disease germs. In practice 

 the heat is applied for only a short time, and as a matter of fact, 

 only a comparatively small number of bacteria are destroyed. 

 The process as usually employed by commercial men merely ac- 

 complishes what is termed " pasteurization." 



The stimulating effects of sterilized soil on plant growth have 

 long been recognized, and some large growers of lettuce and 

 other crops have made extensive use of the practice largely for 

 the effects produced on plant growth. Even as a young boy I 

 remember observing the peculiar stimulating effects sterilized 

 soil had on plant growth where charcoal pits had been burned. 

 The soil and turf used in covering coal pits in the process of 

 making charcoal are steamed and heated for many days, and be- 

 come thoroughly sterilized. When the charcoal is taken out the 

 soil is left spread out, and it often supports a vigorous and rank 

 vegetation. 



The extensive experiments which we made some years ago 

 demonstrated that crops gixnving in sterilized soil are greatly 

 stimulated ; some crops, and lettuce in particular, showing the 

 effects much more than others, however. This stimulation makes 

 a different handling of lettuce necessary, and lower night tem- 

 peratures must be maintained so that the characteristic heads 

 will form properly and topburn be prevented. 



Our experiments showed that while sterilization gives bene- 

 ficial results with certain soils rich in organic matter, other soils 



