74 CROPS AS FEEDERS 



9. What per cent of the total phosphorus in a wheat crop is lost to the soil 

 on the farm when wheat is sold? What per cent of the potassium is sold? 



10. What is the relation between the nitrogen requirement and the protein 



content of crops? Illustrate. What relation is there between the carbo- 

 hydrate content and the potassium requirement of crops? 



11. Name some crops that draw heavily upon the plant-food elements. What 



are the elements required by tobacco in large amounts? 



12. A farmer says that wheat stands up better than oats on a field formerly 



a hog pasture. Explain why. 



13. When grain lodges badly what crops should be grown instead? 



14. What causes lodging of grain, and how may it be prevented? 



15. Discuss alfalfa growing in relation to poor soil. 



16. Is timothy more of a "soil robber" than oats? What do you think of 



tobacco as compared with corn in this respect? 



17. Why can buckwheat and rape grow very well on poor soils? What indi- 



cates a strong feeding power in some plants? Weak feeding power? 



18. Explain why barley requires a richer soil than oats. What is the meaning 



of "rich" soil? 



19. How can the fertilizer needs of any crop on any soil be best deter- 



mined? Why? 



20. Construct a table showing the amounts of "N," "P," "K" and "Ca" 



required to grow a 12-ton corn crop, a 15- ton sugar beet crop, a 15- ton 

 cabbage crop and a 300-bushel apple crop. (See tables.) 



21. How do the root systems of crops differ? 



22. What are root hairs? Explain their function (Figs. 26 and 27). 



23. What knowledge is necessary to grow a crop most successfully? 



24. What is the nitrogen, phosphorus and potassium content 01 an average 



productive silt loam, expressed in per cent? What can you say of the 

 cropping possibilities of soils well supplied with plant-food elements? 



25. Why is not the per cent basis the best for comparing the amount of plant- 



food elements in soils? 



26. Why do peat soils require potash and phosphate fertilizers? 

 27.' How may peat lands be deceptively advertised? Illustrate. 



28. Tell of the nitrogen, phosphorus and potassium contained in subsoils. 



29. What colors of soil and of subsoil have you seen? 



30. See outline summary of this chapter in table of contents. 



