SOIL DISINFECTION 55 



under side at intervals of 6 inches throughout their entire 

 length, may be placed about one foot below the surface 

 of the soil. The pipes should run lengthwise of the bed, 

 18 inches apart, and be connected with a steam boiler 

 capable of producing 80 to 100 pounds' pressure. Before 

 treatment the soil should be thoroughly spaded up and 

 pulverized to permit ready access of the steam to all parts, 

 and all fertilizers except commercial ones should be ap- 

 plied at this time, since fresh spores of the fungus might 

 be carried in if manure were added after disinfection. 



The bed to be treated should be covered with several 

 thicknesses of old burlap or blankets to confine the heat 

 to the soil. The steam should be applied at a pressure 

 of 80 to 100 pounds, since at high pressure it is much drier 

 and the soil is not wet as much as when low-pressure steam 

 is used. A treatment of from one to two hours is usually 

 sufficient thoroughly to disinfect the soil to a depth of 18 

 inches. A few potatoes laid in the surface soil will indicate 

 the thoroughness of the treatment by the degree to which 

 they are cooked. The blankets might advantageously 

 be left on for some time. 



While this method offers some advantages for seed beds 

 of limited area, in that the pipes may be left in the ground 

 and used year after year with little extra labor and may 

 also be used for subirrigation, the initial cost of installa- 

 tion, especially on large seed-bed areas, may be prohibitive. 



Inverted-pan method. — The method which has given 

 the best results in practice, and which because of its simplic- 

 ity and small cost recommends itself for use on large or 

 small areas, is the invention of Mr. A. D. Shamel, of the 

 U. S. Dept. Agr. Bur. of Plant Industry, and was devised 



