40 BULLETIN" 355, U. S. DEPARTMENT OF AGRICULTURE. 
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 J inch 
apart each way. Let each I inch on the horizontal lines represent 25 feet, and each I 
inch on the vertical lines represent 2 feet. 
(b) At grade stake No. 10 the tile was laid 3| feet deep. Determine the fall that 
was available. This line of tile was laid with a uniform gradient. Determine the fall 
in 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. i 
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. AVhat 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? 
