AGRICULTURE FOR SOUTHERN SCHOOLS. 17 
Lesson 21. — Phosphorus and Potassium. 
1. As limiting factors in plant growth. 
2. Nature of the elements and their compounds. 
3. Amount in typical soils — availability. 
Lesson 22. — Soil Fertility. 
1. Views on what fertility is. 
2. Relation to crop production. 
3. Relation to water supply. 
4. Relation to physical condition of soil. 
Lesson 23. — Maintaining Soil Fertility. 
1. History of American agriculture with reference to maintenance of 
fertility. 
2. Relation of soil fertility to national prosperity. 
3. Our duty toward generations to come. 
4. Relation to farm management. 
Special references. — The following Farmers' Bulletins : 257, Soil Fertility. 
406, Soil Conservation. 
Lesson 24. — Commercial Fertilizers. 
1. Development of the fertilizer trade. 
2. Nitrogenous fertilizers. 
Illustrative material : Samples of fertilizing materials and commercial 
fertilizers. (To be used also in lessons to follow.) 
Lesson 25. — Commercial Fertilizers— Continued. 
1. Potash fertilizers. 
2. Phosphate fertilizers. 
3. Mixed fertilizers. 
Lesson 26. — Commercial Fertilizers — Continued. 
1. Buying fertilizers. 
2. Home mixing of fertilizers. 
3. Applying fertilizers. 
Special references. — The following Farmers' Bulletins: 44, Commercial 
Fertilizers. Composition and Use ; 394, Farm Practice in the Use of 
Commercial Fertilizers in the South Atlantic States. 
Exercise 15. — Examination of Commercial Fertilizers. 
Purpose : To aid students in becoming familiar with the form and 
value of common fertilizing materials. 
Directions: Secure samples of the following fertilizing materials 
in glass jars to be properly labeled for future study and use in the 
laboratory: 
Nitrogenous fertilizers : Sodium nitrate, ammonium sulphate, cottonseed 
meal, linseed meal, dried blood, tankage, fish scrap, guano. 
Phosphatic fertilizers : Bone meal, rock phosphate, acid phosphate, basic slag. 
Potassium fertilizers: Muriate of potash, potassium sulphate, wood ashes, 
tobacco stems. 
Secure also samples of as many of the brands of commercial fer- 
tilizers as are commonly sold upon the local market. After the stu- 
73398°— Bull. 521—17 3 
