54 BULLETIN- 355, U. S. DEPAETMENT OF AGRICULTURE. 



REVIEW QUESTIONS, LESSON VII. 



1. How many pounds of phosphorus are there in the surface 8 inches of a silt loam 

 soil if the chemical analysis shows that it contains 0.07 per cent of this element? 



2. State Avays in which phosphorus may be lost from the soil. 



3. How may these losses be replaced? 



4. Why is dairy farming less liable to exhaust the phosphorus of the farm than 

 grain raising? 



5. Name the chief sources of phosphorus used for fertilizers. 



6. Mention the principal kinds of phosphate fertilizers available for use in this 

 country. 



7. "WTiich contains more phosphorus, rock phosphate or acid phosphate? 



8. How should rock phosphate be used? How may acid phosphate be applied? 



9. Do legumes such as alfalfa and clover remove phosphorus from the soil? 



10. How is the phosphorus content of phosphate fertilizers commonly expressed? 



11. In what part of the plant is most of the potassium left when the crop matures? 



12. How does potassium differ in this respect from phosphorus? 



13. How much potassium is usually removed from an acre by a crop of corn? 



14. What plants draw most heavily on this elejnent? 



15. How does the amount of potassium compare with that of phosphorus in ordinary 

 clay loam soil? 



16. 'WTiat kinds of soil are most lacking in potassium? 



17. What is the chief source of potassium fertilizers, and what are the most im- 

 portant kinds? 



18. About how much muriate of potash would you apply to muck soils on which you 

 expected to grow a heavy crop of cabbage? 



19. When should muriate of potash be applied to ground on which potatoes are to 

 be planted? 



20. Under what conditions is it unnecessary to use potassium fertilizers on heavy 

 soils? 



LESSON VIII. MANURES AND FERTILIZERS. 



In the general use of the terms, manures are thought of as the 

 waste materials from the care of live stock, while fertilizers include 

 commercial materials of value to the soil because of their nitrogen, 

 phosphorus, and potassium content. In this lesson we shall include 

 as manures crops which are grown and returned to the soil, either in- 

 directly through animal excrement and straw or other material used 

 as bedding, or directly by returning the crop without harvesting 

 solely for purposes of soil improvement. These subjects wiU be 

 treated, respectively, under the headings of barnyard manure and 

 green manures. The use of manures as soil builders has a distinctive 

 advantage over commercial fertilizers because of the value which re- 

 sults from the decaying vegetable matter in addition to the nitrogen, 

 phosphorus, and potassium which theyfurnish to the soil. Commercial 

 fertilizers stimulate the growth of plants by supplying the three es- 

 sential elements noted above in a concentrated and usually available 

 form. The intelligent combined use of the two is best for both soil 

 and crops. 



