6) VEGETABLE FORCING 
the soil every year as a matter of insurance, though there 
may be little evidence of the presence of destructive 
insects or diseases. Others. practice sterilization only 
when they regard it as absolutely necessary, and they 
may have large ranges in which the soils of some houses 
are sterilized every year, and others in which the soils 
have never been sterilized. Conditions are so variable 
that no rule can be laid down for all growers in regard to 
the desirability or importance of soil sterilization. It is 
certain, however, that hundreds of growers will be com- 
pelled to resort to this practice unless desiccation (for 
Fig. 29.—Pan steam sterilization in operation at the Indiana Agricultural 
Experiment Station. 
nematodes) and mulching are found to be satisfactory 
and become more generally employed. 
Methods.—Although dry heat and hot water are em- 
ployed to some extent, steam and the formalin or for- 
maldehyde drench are the methods in most general use: 
of these two methods steam is very much the more 
popular in the largest commercial establishments, though 
the hot water method is gaining in popularity. Steam- 
ing, when properly managed, destroys all animal life as 
well as fungous and bacterial enemics. The nematode, 
