Treatment of Sick Soils 



39 



growers shove the iron pipe down into the soil six 

 inches; others hold it above the surface of the soil. 

 The water penetrates equally well either way, be- 

 cause the soil is in a loose condition and the water 

 goes out under pressure. There are no figures as to 

 the exact amount of water per cubic foot of bed sur- 

 face, but hot water is applied until it stands on the 

 surface of the soil in pools and will no longer pene- 

 trate. The exact amount will, of course, vary with 

 the physical condition of the soil and its relative 

 dryness. The greenhouse men do not practice cover- 

 ing the soil with anything to hold in the heat. 

 Out of doors, however, a cover would be desirable 

 because of wind currents. Three or four days after 

 treatment, the soil is cool enough and dry enough 

 to plant." 



It will require about two days for five men to 

 treat a house 275 feet by 34 feet. 



Roasting or Fan Firing. By this method, the 

 soil to be sterilized is removed from the bed and 

 placed in a pan, over a hot fire. After roasting, 

 the soil is returned to the bed and more of it steril- 

 ized. This method is too slow and has the disad- 

 vantage, besides, of destroying the humus in the 

 soil. The advantage of steam sterilization and of 

 the ''fire" methods lies in the destruction of all 

 weed seed, together with the fungi which cause 

 damping-off (fig. 7, a and b.). 



