122 A YEAR IN AGRICULTURE 



3. What are the types of soil of your local community? 



4. Show how water may be a limiting factor in the pro- 

 duction of the maximum crops. 



5. What is meant by active organic matter in the soil? 



6. Give some values of cultivation of soil. 



7. What is meant by a live soil? 



8. Name the ten plant-food elements and give their com- 

 mon source. 



9. Which elements are most abundant and which are likely 

 to be deficient? 



10. What farm crops are the heaviest feeders on soil fer- 

 tility? 



11. What is meant by available plant-food in the soil? 



12. How is plant-food lost from the soil? 



13. What is meant by green manure, and what is its value ? 



14. Mention all the values of organic matter in soil fer- 

 tility. 



15. What are the most economic sources of nitrogen, phos- 

 phorus, and calcium in systems of permanent soil fertility ? 



16. Compare the cost of commercial forms of nitrogen 

 with the natural source in legume crops. 



17. Compare the cost of acid phosphate with raw rock 

 phosphate. 



18. What is meant by complete fertilizer? 



19. Explain why the Poorland Farm mentioned in the 

 preceding chapter was poor land. What were the essential 

 steps in restoring this farm? (The answer to this question 

 should be an explanation of a system of permanent soil fer- 

 tility.) 



20. (a) To produce 100 pounds of grain requires about 

 3 pounds of nitrogen, of which 2 pounds are deposited in 

 the grain itself and 1 pound in the straw or stalks. 



(b) In live-stock farming one-fourth of the nitrogen in 

 the food consumed is retained in the animal products meat, 



