THE COST OF RESTORING PLANT FOOD 47 



EXERCISE 



1. How many pounds of plant food are required to grow 

 18 A. of corn, averaging 50 bu. to the acre ? 



2. How many pounds of plant food are required to grow 

 18 A. of clover, averaging 2 tons to the acre ? averaging 

 1 ton to the acre ? 



3. What is the tax upon the soil in growing a 50-acre 

 field of wheat, averaging 20 bu. to the acre ? 



4. What is the value of the plant food removed from the 

 soil in growing 50 bu. of corn, nitrogen being quoted in the 

 market at 22$ a pound, phosphoric acid at 5$ a pound, and 

 potash at 6$ -a pound ? 



5. A father tells his son that he may have all the wheat 

 he can grow on a 10-acre field if he will pay, at commercial 

 prices (see problem 4), for the plant food removed from the 

 soil. If the son grows 20 bu. per acre, how much does he 

 owe his father ? 



THE COST OF RESTORING PLANT FOOD TO 

 THE SOIL 



55. Nitrogen, phosphoric acid, and potash may be re- 

 turned to the soil by means of commercial fertilizer, straw, 

 and manures. 



56. The table on the following page gives some idea of 

 how plant food may be returned to the soil, and what it 

 is worth per ton at commercial prices : nitrogen, 20$ per 

 pound ; potash, 5$ ; and phosphoric acid, 5$. 



Pupils should complete the table with values based on 

 commercial prices, and make a duplicate copy on a large 

 piece of pasteboard for their parents to inspect and to keep 

 for future reference. 



