174 SOILS AND FERTILIZERS 



Phosphoric acid 

 per acre. 



Lbs. 



Barley, 40 bu 15 



Straw, 3,000 lbs 5 



Total 20 



Oats, 50 bu 12 



Straw, 3,000 lbs 6 



Total 18 



Corn, 65 bu 18 



Stalks, 4,000 lbs 4 



Total 22 



Peas, 3,500 lbs 25 



Red clover, 4,000 lbs 28 



Potatoes, 150 bu 20 



Flax, 15 bu 15 



Straw, 1 ,800 lbs 3 



Total 18 



210. Amount of Phosphoric Acid in Soils. — To 



meet the demand of growing crops (for 25 pounds of 

 phosphoric acid per acre), there is present in soils from 

 1,000, and less, to 8,000 pounds of phosphoric acid per 

 acre, of which, however, only a fraction is available as 

 plant food at any one time. The availability of phos- 

 phoric acid is a factor which has a great deal to do in 

 determining crop-producing power. Many soils contain 

 a large amount of total phosphoric acid, which has be- 

 come unavailable because of poor cultivation and the 



