STEAM STERILIZATION OF SEED BEDS. 5 



selected for the seed bed. It has been practiced for a great many 

 years in the tobacco-growing areas south of Maryland and Ohio, 

 where it is common to locate the seed bed at the edge of or in the 

 woods. The area selected for use as a seed bed is cleared, the ground 

 broken, and brush and wood laid over it and burned. The degree of 

 thoroughness with which the surface burning is done in different 

 sections depends on the character and quantity of the fuel supply 

 and on other local conditions. When the burning is done thoroughly 

 the resulting heat is sufficient to free the soil of all fungi and weed 

 seeds to a depth of several inches, but the organic matter of the soil 

 is largely destroyed, and later the surface of the bed is likely to bake 

 during even short dry periods, killing a large percentage of the 

 seedlings. 



Barn manure and fertilizers containing organic matter must be 

 applied after firing to prevent their decomposition in the burning, 

 and this opens the way for adding to the seed bed material carrying 

 fungous spores or weed seeds. If excessive quantities of ashes are left 

 on the bed the growth of the seedlings may be affected, and sometimes 

 the germinating seed may be killed. 



In order fully to accomplish the purpose of burning, it is necessary 

 to secure a high heat over the surface of the entire seed bed. - This 

 requires large quantities of wood, and the ever-increasing scarcity of 

 wood in certain localities has made it practically impossible longer 

 to pursue this method. 



A modification of the open-fire method is found in the portable 

 wood-burning furnace. This furnace consists of a heavy fire box, 9 

 feet long, 3 feet wide, and 18 inches deep, constructed of iron and set 

 close to the ground. On top of this is set a pan 9 by 3 feet and 

 10 to 12 inches deep. The whole apparatus rests at one end on a pair 

 of wheels and at the other end on two legs. It is furnished with two 

 handles for lifting and drawing. A fire is made in the fire box and 

 the soil from the seed bed, to a depth of 4 or 5 inches, is shoveled into 

 the pan and covered. The heat from the fire below brings about 

 thorough serilization. While more effective than the open fire on 

 the bed, the furnace has the disadvantage of being slow in operation 

 and equally expensive in fuel consumption. It also necessitates a 

 second handling of the soil. 



THE STEAM-PAN METHOD OF STERILIZATION. 



The steaming of the soil is the most satisfactory method of steriliza- 

 tion \vhich has been developed up to the present time. The direct ap- 

 plication of the steam to the soil by means of an inverted pan or hood 

 has now been in successful operation for a number of years. 1 Thus far 



1 This method has been briefly discussed in Farmers' Bulletin 343, " The Cultivation of 

 Tobacco in Kentucky and Tennessee" (1909), and in Bureau of Plant Industry Bulletin 

 158, " The Root-Rot of Tobacco Caused by Thielavia Basicola " (1909). 



