Cultivation and Drainage 



53 



until about one hundred years ago. The modern plow is 

 better than the ancient plow because it not only loosens 

 the soil but turns the earth upside down, covering any 

 scattered trash or manure. It exposes the bottom of 

 the " furrow slice " to the influence of sun and air. 



Very deep plowing is usually beneficial, for it loosens 

 a large quantity of soil in which the roots may search 

 for nourishment and into which rain can readily be 

 absorbed. However, the plow should not be run at the 

 same depth every year, for its pressure and the trampling 

 of the horse in the furrow will, in time, make a hard 

 layer, called a " plow sole," at this level. This plow 

 sole is a sort of artificial hardpan, through which the 

 roots cannot easily grow. Plowing at a different depth 

 each year will prevent the plow sole from forming. At 

 a California experiment station the crop was nearly 

 doubled in one year by plowing deep enough to break 

 up the plow sole. 



Plowing the ground when it is very wet injures it badly, 



Advantages 

 of the mod- 

 ern plow 



Deep 

 plowing 



Avoiding 

 a plow sole 



John Deere Plow Co. 



PiG. 34. A disk plow is used to work soil which is so sticky that an 

 ordinary plow will not turn it. 



