16 BULLETIN 521, U. S. DEPARTMENT OF AGRICULTURE. 
Lesson 18. — Erosion of Soils. 
1. Nature of erosion. 
2. Problem of erosion in the South. 
3. Conditions influencing erosion. 
4. Wind erosion. 
Illustrative material: An erosion model. (See U. S. Dept. of Agriculture, 
Office of Expt. Stas. Circ. 117, Working Erosion Model for Schools.) 
Lesson 19. — Prevention of Erosion. 
1. Relation to crops grown. 
2. Relation to soil management. 
3. Contour planting. 
4. Terracing. 
Special references : The Mangum Terrace in its Relation to Efficient Farm 
Management. U. S. Dept. of Agriculture, Bur. PI. Indus. Circ. 94. An 
Effective Method of Preventing the Erosion of Hill Land. U. S. Dept. 
of Agriculture, Bur. PI. Indus. Circ. "A" 78. Economic Waste from 
Soil Erosion. U. S. Dept. of Agriculture Yearbook, 1913. 
Exercise 14. — A Field Study of Erosion and Methods of Control. 
Purpose : To make students familiar with the causes of erosion and 
the most efficient methods of control w T hich will apply to local 
conditions. 
Directions : In connection with a study in the classroom of soil 
erosion and methods of control the class should visit a near-by field 
that has become gullied and bare through washing, and on the same 
trip, if possible, visit farms upon which erosion has been prevented 
by methods best suited to the section. 
Record and report: Each student should make a written report of 
the trip in which he should bring out, in addition to any notes of 
special interest, answers to such of the following questions as may 
apply: Why has the washing been especially bad upon the field 
visited ? At what season of the year is the washing the worst? What 
methods of prevention or control would have been best suited to this 
field? To what extent is erosion prevented on the farms visited by 
proper plowing and cultivation? What have the methods of plant- 
ing to do with erosion and its prevention? What have the systems 
of cropping and the kind of crops to do with succession in prevention 
and control of erosion? What kind of terraces appear to be best 
suited to this section? To what extent are open ditches and tile 
drains used to advantage? What suggestions do you have for 
improvement of the methods used ? 
Lesson 20. — Nitrogen as Plant Food. 
1. Nature of the element. 
2. Why nitrogen is valuable. 
3. Sources of nitrogen in the soil. 
4. Nitrification and denitrification, 
5. Relation to leguminous plants. 
