40 BULLETIlSr 355, U. S. DEPARTMENT OF AGEICULTURE. 



below the grade stake No. at the top of the ditch. The elevations above datum plane 

 at the grade stakes are as follows: No. 0, 52 feet; No. 1, 52 feet; No. 2, 52.5 feet; No. 3, 

 52.75 feet; No. 4, 53.25 feet; No. 5, 54.25 feet; No. 6, 53.75 feet; No. 7, 54 feet; No. 8, 54 

 feet; No. 9, 54 feet; and No. 10, 53 feet. 



(a) Draw a profile or cross section of the ditch and ground, showing the line of 

 elevation of the surface of the ground. Use ruled paper having lines drawn I inch 

 apart each way. Let each { inch on the horizontal lines represent 25 feet, and each J 

 inch on the vertical lines represent 2 feet. 



(b) At grade stake No. 10 the tile was laid 3f feet deep. Determine the fall that 

 was available. This line of tile was laid with a uniform gradient. Determine the fall 

 ill inches per hundred feet. 



(c) Determine the grade line, or the height of the bottom of the ditch above the out- 

 let at each grade stake. (Ref. No. 8, pp. 72-74.) Set these elevations down in a col- 

 umn opposite the elevations of the surface of the ground at each grade stake. 



(d) Determine the depth of cut that was made at each grade stake. (Ref. No. 8, 

 pp. 77-82.) 



(e) On the profile map draw a line 5 feet above and parallel with the grade line 

 from stations No. to station No. 10. Let this line represent the line of sight formed 

 by the string to aid in the construction of the ditch. (See p. 37.) Determine the 

 height the string should be above each grade stake. 



Field excursions. — (a) By the use of any convenient thermometer, the temperature 

 of various soils may be compared; north slopes with south slopes, black and light 

 colored soils, upland and lowland, drained and undrained lowland, sandy soil and clay 

 or silt loam, loose and compact clay or silt loam. Explain all variations found. 



(b) If convenient, make a trip to inspect some drainage systems. Make a sketch 

 of the drained area and draw in the drainage system. 



If convenient, in the spring compare the temperature of the soil above a line of 

 tile with that midway between laterals. 



Observe the natural drainage of any interesting area. 



REVIEW QUESTIONS, LESSON V. 



1. How is soil temperature related to fertility and the growth of crops? 



2. Explain fully what becomes of the heat which is absorbed by the surface of the 

 soil. 



3. What factors influence the amount of heat which penetrates the subsoil? 



4. Explain why frosts sometimes occur on poorly drained ground when they do not 

 occur on well-drained ground? 



5. Discuss the practical means of regulating soil temperature. 



6. State several benefits which may be derived by good drainage of soils. 



7. How can you tell whether the soil of a given field is well drained or not? 



8. Describe a good method for the surface drainage of flat land which is nearly level. 



9. Why is underdrainage by the use of tile more to be desired than surface drain- 

 age? 



10. How does the water from the surface find its way into lines of tile? 



11. What kind of soil is most difficult to drain by means of tile? 



12. Estimate the slope in feet per mile necessary to permit good tile drainage on an 

 80-acre field? 



13. What should the diameter of a main outlet of tile be on a field of 100 acres having 

 a slope of 1 inch to 100 feet? 



14. Define grade stakes, line of levels, grade line. 



15. How should tile be laid? What is meant by blinding tile? 



