90 VEGETABLE FORCING 



Instead of the soil in the pots all being heated to 212 degrees they 

 received the following various degrees of heat before planting : 



No. of pot 12 34 567 8 9 10 11 12 



Temperature 114 118 127 140 147 150 159 161 163 163 170 176 



"Result: Nos. 1, 2 and 3 all damped off. The remainder were 

 perfectly free from the damping-off fungus and nematodes. 



"Exp. d. Sixteen pots of cucumbers were treated the same as *c.' 



No. of pot 1 23 4 5 6 7 8 9 10 11 12 13 14 15 16 



Temperature 147 149 154 159 163 167 16? 172 176 183 185 186 192 194 196 199 



"Result : No nematodes. 



"From these experiments, which only represent about one-half 

 of what was done, it appears that a very high temperature is not 

 necessary in order to free infested soil of nematodes. The number 

 of degrees of heat necessary is about 140 degrees, but as a matter of 

 safety the temperature should go above this, inasmuch as in large 

 areas of soil the distribution of heat is always unequal, and while 

 one portion may be heated as high as 190 degrees another portion 

 may not exceed 110 degrees. The conclusion, then, that the soil 

 must be heated under pressure to a temperature of 225 or 235 de- 

 grees in order to kill nematode life is therefore not valid in all 

 cases. These experiments were made with sufficient care and were 

 repeated often enough with the same results to consider them trust- 

 worthy." 



Stone has since stated, and his statement is based upon 

 further research, that the soil should be heated to a 

 temperature of 180 degrees and that 212 degrees is better. 

 This corroborates the views of growers who have been 

 successful in steaming soils. While 140 degrees will 

 kill insects and nematode eggs, there are disease germs 

 which require higher temperatures. A high temperature 

 is also necessary to secure the thorough permeation of 

 the soil particles which harbor and protect insects and 

 disease germs. 



Time required. Steam sterilization is really the cook- 

 ing of every particle of soil, and considerable time is 

 required to accomplish this. Steam under pressure 

 passes through open, coarse, sandy soils more rapidly 



