62 



FIELD CROP PRODUCTION 



film moisture. The breaking up of the soil into fine 

 particles also permits the air to enter the soil more freely 

 and thus supply the root cells with oxygen, which they 

 require just as do those plant cells above ground. Plants 

 obtain their food by means of root hairs which are so 

 delicate that they cannot penetrate the soil particles, but 

 grow around them. Thus a soil composed of many fine 



Fig. 16. — Plowing with a tractor. 



particles provides greater feeding area for the plant than 

 one made up of large particles. Another purpose of 

 plowing is to incorporate with the soil the organic matter 

 that it has accumulated on the surface or that is applied 

 in the form of manure or by growing a green manure crop. 

 The organic matter when mixed with the soil not only 

 supplies it with plant food, but improves its physical 

 condition, permitting better aeration and increasing its 



