EXTENSIOISr COUESE IIST SOILS. 79 



nitrogen per acre from the growth of vetch: Determine the nitrogen balance to the 

 soil of a field resulting from one period of the cropping system, not including alfalfa. 

 (See table 23, Ref. 5, p. 154). What would be the result if cowpeas were grown 

 in the corn and added 30 pounds of nitrogen to the soil each year? 



(b) If the farmer feeds to live stock three-fourths of all produce grown, including 

 alfalfa, and uses one- fourth for bedding; and if one- third of the organic matter fed is 

 recovered in the manure, and if three-fourths of the nitrogen and three-fourths of the 

 phosphorus likewise are retained from the feed and bedding; determine the balance of 

 humus and nitrogen to the farm in any period of five years, resulting from this system. 

 (Each ton of alfalfa grown may be considered as fixing 40 pounds of nitrogen from the 

 air.) Compare this balance -with, the one obtained in (a). 



(c) Figure how much phosphorus would be removed from the farm during each 

 5-year period from both the grain farming and the live-stock farming. How much 6 

 per cent acid phosphate would have to be added every five years to balance the amount 

 of phosphorus removed? 



11. Consider your own system of farming and figure a balance from the standpoints 

 of humus, and the plant-food elements, nitrogen, phosphorus, and potassium. 



REVIEW QUESTIONS, LESSON XI. 



1. Why has sandy soil little ability to conduct water upward from lower layers? 



2. Why is it true that sandy soils may use the water of a light rainfall more efficiently 

 than heavy soils? 



3. Explain why topography must be considered more carefully in the case of sandy 

 soils than in the case of clay soils, especially in climates of moderate rainfall. 



4. Explain why rolling a sandy soil aids in the germination of fine seeds. 



5. In what ways may the injury due to blowing of sand be lessened or prevented? 



6. What are the two chief causes of low fertility in sandy soils? 



7. How can the nitrogen supply of a sandy soil be best increased and maintained? 



8. What advantages has a sandy soil over a heavj^ soil? 



9. What small grains are especially well adapted to sandy soils? Explain. 



10. To what classes of crops are sandy soils best adapted? 



11. What is meant by heavy clays? 



12. Describe how heavy clay soils may be formed. Give examples. 



13. Name some of the characteristics of clay. 



14. Discuss methods of maintaining good tilth on heavy clay land. 



15. Explain why grasses and cereals are best adapted to these soils. 



16. Why are heavy soils particularly objectionable for the growing of potatoes? 



17. Why do most crops on heavy clay soils respond well to the use of phosphate 

 fertilizers? 



18. Why do some clays contain more organic matter than others? 



19. When a clay soil is black, does it necessarily mean that it is well supplied with 

 available nitrogen? Explain. 



20. Do clay soils ever require lime? 



21. What are marsh soils, and how are they formed? 



22. Distinguish between muck and peat soils. 



23. What factors should govern the construction of open ditches? 



24. What precaution should be taken in laying tile in a peat marsh? 



25. What are the peculiarities of marsh soils as a class in regard to fertility? 



26. Explain why some marsh soils are acid and others are not. 



27. How may the fertilizer needs of marsh soil be best supplied? 



28. In what ways is the looseness of marsh soils unfavorable to the growth of crops, 

 and how may it be overcome in part? 



29. What crops are especially well adapted to marsh soils, and why? 



