CHAPTER VI 

 SOIL STERILIZATION 



The necessity of sterilization. In the great commer- 

 cial forcing establishments the soil is not changed, but 

 it is used over and over again with yearly additions of 

 stable manure. The amount of vegetable matter in- 

 creases and the physical properties improve so that in 

 most instances there are serious objections to changing 

 the soil aside from the labor of moving it. As previously 

 stated, vegetable forcing is the most intensive branch of 

 olericulture. Crops follow each other in quick succes- 

 sion. There may be no rotation whatever, for often the 

 same crop is grown year after year. With such a system 

 of cropping there is naturally an accumulation of 

 destructive parasites. 



Continuous cropping in the open ground nearly always 

 leads to trouble, and the conditions of the greenhouse are 

 even more favorable for the breeding and multiplication 

 of all classes of parasitic enemies. The accumulation of 

 soil organic matter is equally advantageous to insect life 

 and to fungous foes. Soil desiccation, inundation, freez- 

 ing, spraying, mulching and fumigating have their values, 

 and may be the means of checking or even controlling 

 many of the foes, but other measures have become a 

 necessity in most of the large commercial houses. In 

 fact, soil sterilization is now universally regarded as 

 essential to success, although there are instances where 

 splendid crops have been grown for many years without 

 resorting to sterilization. 



There is a wide difference of opinion among successful 

 and intelligent growers regarding the value of steriliza- 

 tion. Some consider it an essential operation to sterilize 



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