98 



VEGETABLE FORCING 



and most growers feel that it is unwise to take chances 

 of losses that can be averted by proper methods of 

 disinfection. 



After-treatment. Soils that have been sterilized by 

 either steam or formalin require careful after-treatment. 

 This is particularly true of silty and clay soils, the 

 structure of which is affected by these treatments. 

 They become more compact, and their water-holding 

 power is increased so that there is danger of overwater- 

 ing such soils until normal relations become established. 

 As soon as dry enough the surface of the ground should 

 be stirred and water applied with extreme caution after 

 the plants have been set. 



7777 



Formalin Sterilization 



Strength of solution. Most growers who employ this 



method of steri- 

 1 i z a t i o n use 

 either three or 

 four pints of 

 commercial for- 

 malin of 40 per 

 cent purity to 

 50 gallons of 

 water. Two 

 pints often 

 prove effective, 

 but a stronger 

 solution is gen- 

 erally pre- 

 ferred. Rhizoc- 

 tonia or rosette 

 of lettuce may 

 be controlled 

 with less than 

 two pints to 50 



Out/et 



(Z 



In/et 



Fig. 33. Apparatus for formalin sterilization. (W. T. 

 Water tank. F. T. Formalin tank. G. Water-glass 

 gauge to show quantity of formalin. A. Air cock. V. 

 Valve. F. Funnel. . Air pipe to maintain same 

 pressure in both tanks. D. Drain-off cock. H. and 

 R. Supports. B. Base. O. Outlet. S. Glass tube 

 through which the formalin drops to tank below.) 



