86 



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 Indh 

 Experiment Station. 



Agricultural 



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 enemies. The nematode, 



