28 



SOILS AND FERTILIZERS 



very largely of clay. There are subsoils in the western 

 states which have clay-like characteristics but contain 

 only about 15 per cent of clay, the larger part of the 

 soil being silt. A loam soil is a mixture of sand and 

 clay ; if clay predominates, it is a clay loam, while if 

 sand predominates, it is a sandy loam. 



RELATION OF THE SOIL TO WATER AND AIR 



18. Amount of Water required by Crops. Experi- 

 ments show that it takes from 275 to 375 pounds of 

 water to produce a pound of dry matter in a grain crop. 

 In order to produce an acre of average wheat, 350 tons 

 of water are needed. The amount of water required 

 for the production of an acre of various crops is as 

 follows : 12 



AVERAGE AMOUNT 

 TONS WATER 



MINIMUM AMOUNT 

 TONS WATER 



Clover . 

 Potatoes 

 Wheat . _. 

 Oats . . . 

 Peas ". . 

 Corn . . . 

 Grapes . 

 Sunflowers 17 



400 

 400 



300 

 300 



The amount of water required for the production of 

 crops in humid and arid regions has not been exten- 



