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ELEMENTS OF AGRICULTURE 



air and heat; and from these they supply the world 

 with food. Like all good workers they demand a good 

 supply of material, and a comfortable shop well sup- 

 plied with fresh air and water. A soil without bacteria 

 is as dead as a desert, and incapable of producing 

 plants. 



Questions 



1. How does the loss of mineral matter affect the fertility 

 of soil? 2. Name three mineral elements which sometimes 

 hecome exhausted. 3. About how much phosphoric acid is 

 removed from the soil by 500 pounds of ordinary hay? 

 4. How are the unavailable phosphates changed into plant 

 food? 5. Why is it an easy matter to exhaust the supply 

 of available phosphates in ordinary soil? 6. Why is it that 

 available phosphates are not held in the soil? 7. Explain 

 why the supply of phosphates in the soil is not exhausted. 

 8. Why do cultivated crops take from the soil more plant 

 food than crops growing naturally? 9. How far do the 

 roots of most plants penetrate the soil? 10. How does 

 potash in the soil become available to plants? 11. What 

 changes the unavailable potash into available compounds? 

 12. How is lime useful to the bacteria in the soil? 



PROBLEMS 



1. If a soil weighs 100 pounds to the cubic foot and con- 

 tains 0.15 per cent of phosphoric acid, how many, pounds of 

 phosphoric acid are contained in an acre of such soil 12 

 inches deep? 



2. Calculate the amount of potash in an acre of soil 12 

 inches deep when it weighs 95 pounds per cubic foot and 

 contains 0.3 per cent potash? 



