54 BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
REVIEW QUESTIONS, LESSON VH. 
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 ways 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. 'Which 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 element? 
15. How does the amount of potassium compare with that of phosphorus in ordinary 
clay loam soil? 
16. What 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? 
IS. 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 Vin. 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 will 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 they furnish 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. 
