SOIL STERILIZATION 93 



larger. They were placed 12 to 15 inches apart and 

 closed at the ends opposite the headers. The holes in the 

 pipe were usually l /% or l /^ inch in diameter, about a foot 

 apart, and turned down to prevent them from being 

 stopped with dirt. It is probable that the boxes should 

 never be more than a foot deep. Two-inch drain tile may 

 be substituted for iron pipe. With an ample volume of 

 steam under high pressure thorough sterilization can be 

 effected in an hour. The boxes may be covered with 

 heavy canvas or hotbed sash. When a large amount of 

 soil is to be sterilized there should be at 'least two boxes 

 to facilitate handling the soil. While the box method is 

 convenient for sterilizing potting soils, flats, tools, etc., it 

 is now seldom used in vegetable-growing establishments 

 because of the excessive cost of handling the soil. 



Pans. The inverted pan method is used by a great 

 many large growers, especially in the Cleveland district. 

 It is regarded by some as not so thorough as the tile and 

 perforated pipe plans, although some of the most careful 

 and successful growers are unwilling to concede this 

 point. There are examples of perfect pan sterilization of 

 soils which had become most seriously infested with 

 nematodes and many other destructive pests. The pan 

 method does not require any handling of the soil, and 

 this is unquestionably its greatest advantage. The plan 

 is becoming more popular every year. It is particularly 

 valuable for open, porous soils which are easily pene- 

 trated by steam. 



Galvanized iron pans are the most durable. They may 

 be of any convenient size. Fig. 29 shows a pan which is 

 used at Purdue University. Sometimes they are only 

 4 feet wide and 8 to 12 feet long. The pans are usually 

 6 to 8 inches deep. Pipe connection is made at the side 

 or end as shown in the illustration, or in the bottom of 

 the middle of the sterilizer with an ell and a nipple on the 

 outside for the attachment of a hose of inch size or larger. 



