328 SOILS AND FERTILIZERS 



29. Why is it necessary to cultivate the soil after a rain ? 30. Ex- 

 plain the movement of the soil water after a light shower. 31 . What 

 influence has rolling the land upon the moisture content of the soil? 

 32. What is subsoiling and how does it influence the moisture 

 content of soils ? 33. What influence does early spring plowing 

 exert upon the soil moisture ? 34. What is the action of a mulch 

 upon the soil ? 35. Why should different soils be plowed to differ- 

 ent depths ? 36. What is meant by the permeability of a soil? 

 37. How may cultivation influence permeability? 38. How may 

 commercial fertilizers influence the water content of soils ? 39. 

 Explain the physical action of well-prepared farm manures upon the 

 soil and their influence upon the soil water. 40. What is the object 

 of good drainage ? 41. Why does deforesting a region unfavorably 

 influence the agricultural value of a country ? 42. What are the 

 sources of heat in soils ? 43. To what extent does the color of 

 soils influence the temperature ? 44. What is the specific heat of 

 soils? 45. To what extent does drainage influence soil tempera- 

 ture and how does cultivation affect soil temperature ? 46. How 

 do manured and unmanured lands compare as to temperature ? 47. 

 What relation does heat bear to crop growth ? 48. What materials 

 impart color to soils ? 49. What is the effect of loss of organic 

 matter upon the color of soils ? 50. What materials impart taste to 

 soils ? Odor ? 51. What effect does a weak current of electricity 

 have upon crop growth ? 52. Do all soils possess the same power 

 to absorb gases ? Why ? 



CHAPTER II 



53. What is agricultural geology ? 54. What agencies have 

 taken part in soil formation? 55. How does the action of heat, 

 cold, air, and gases aid in soil formation ? 56. Explain the physical 

 action of water in soil formation. Explain its chemical action. 57. 

 What is glacial action, and how has it been an important factor in 

 soil formation ? 58. Explain the action of earthworms and vegeta- 

 tion upon soils. 59. How have micro-organisms aided in soil forma- 



