soil, SESSION. 



145 



of faith. The result is that a thousand apply the truth where one did 

 before, and there is perhaps no discovery in all the wide realm of ag- 

 riculture which will be able to do so much in the permanent winning of 

 bread as this. 



I wish now to emphasize for your stronger conviction three other 

 very fundamental truths upon which enduring economic methods of soil 

 management must forever rest. These are : 



Fig. 1.— Showing the relative amounts of dry soil ; soil air ; total plant food and 

 plant food materials soluble in water contained in one cubic foot of average surface 

 soil in the United States. 



I. The necessity for a sufficient amount of room in the soil, not 

 only in the portion turned with the plow, but throughout the effective 

 root zone. 



2. The existence in the soil of large amounts of plant food ma- 

 terials, but not in available forms, and which it must become the business 



A -10 



