SOIL STERILIZATION 87 



which is considered the most serious of the animal foes, 

 is repressed both in the egg and worm state by thorough 

 steaming. Weed seeds are also destroyed and plant 

 food is made more available. Several investigators have 

 shown that steam sterilization increases the amount of 

 soluble or available nitrogen, potash and phosphoric 

 acid. It also increases the absorptive power of the soil 

 for water. Some of the experiments indicate that steam 

 sterilization tends to develop certain toxics and also in- 

 creases the acidity of the soil. If lime, however, is 

 applied before the soil is sterilized, there need be no fear 

 of any harmful effect. 



In this connection, Stone and Smith state the follow- 

 ing in Bulletin 55 of the Massachusetts station : "In the 

 numerous crops of cucumbers, tomatoes and lettuce 

 which we have grown in sterilized earth we have never 

 noticed anything of a detrimental nature, but on the 

 other hand a decidedly beneficial effect as the result of 

 sterilization. Not only is this shown in the difference in 

 color which the plants take on, but in an appreciable 

 acceleration of their growth. We have repeatedly run 

 parallel cultures of sterilized and unsterilized soil and 

 have invariably noticed these effects on cucumbers and 

 lettuce." 



Rudd, whom we have already quoted as having tried 

 the sterilized method, says :* 



"It has long been known among practical gardeners that heating 

 the soil produces beneficial results. Every greenhouse soil contains 

 humus or vegetable mold, and it is recognized by vegetable physiol- 

 ogists that the presence of humus in the soil plays an important 

 part in the assimilation and plant growth, but its efficiency depends 

 partly upon the stage of decomposition at which it has arrived. It 

 has been shown by experiments in which plants are treated in one 

 case with humus in the raw condition, and in the other with humus 

 which has been subjected to the action of steam for several hours 



* American Florist, Vol. IX, p. 171-197. 



