84 THE BOOK OF CORN 



The plant food in the soil is liberated for the use 

 by the plants through the agency of soil organisms 

 and chemical action. The organisms require oxygen 

 in their process of development. Therefore the air 

 must circulate freely in the soil in order that these 

 organisms may carry on their work. In the germina- 

 tion of the seed, oxygen is absolutely necessary, so that 

 air must be present for the first process of germination 

 to begin. For instance, it frequently happens that 

 directly after the planting on a clay soil, a heavy dash- 

 ing rain packs the surface soil so that little air can 

 enter. The seed will germinate very imperfectly even 

 though the other conditions of germination be fully 

 supplied. 



It is never advisable, even in the heavy clay soils, 

 to greatly vary the depth of plowing in any one season. 

 If the soil has been turned to a certain depth during its 

 previous cultivation, and then some one season it is 

 plowed several inches deeper than ordinary, a layer of 

 cold soil will be turned up for the young plants to feed 

 upon. If this is done in the fall the action of the 

 weather in freezing and thawing corrects the mechani- 

 cal condition and puts the plant food in usable form 

 before a crop is grown. However, if this deep plowing 

 is done in the spring, the young plants are unable to 

 use the plant food in this layer of soil and are con- 

 sequently checked in their growth. This frequently 

 results in an almost complete failure of the crop. 



This is illustrated in the history of the cultivation 

 of the sugar beet in Illinois. Before the culture of the 

 crop was thoroughly understood, it was thought neces- 

 sary to plow very deep in order to furnish a loose seed- 

 bed. As a result, most of the fields were plowed several 

 inches deeper than ordinary. The seed was planted in 

 this layer of cold soil and the young plants attempted 

 to secure nourishment from this source. As this soil 



