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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