xiv CONTENTS 



XII. NITROGEN, PHOSPHORUS AND POTASSIUM IN RELATION TO SOIL 



FERTILITY 187 



1. Fertilization and the Theory of Fertilizers. 2. Green , 

 manuring: (a) Green manuring and its benefits. (6) Crops 

 for green manuring legumes best, (c) Plowing under the 

 crop when, how and for what crops, (d) Feeding vs. plow- 

 ing under the crop, (e) Some hints on green manuring. 



3. Commercial Fertilizers: (a) Four classes of commercial 

 fertilizers. (6) Nitrogen fertilizers and their value. Legumes 

 to solve nitrogen problem, (c) Phosphate or phosphorus 

 fertilizers and their uses, (d) Potash or potassium fertil- 

 izers and their value, (e) Mixed fertilizers. (/) Concerning 

 commercial fertilizers in general, (g) Soils and crops deter- 

 mine kind to use. (A) Home mixing of fertilizers, (i) How 

 commercial fertilizers may be applied. (j) Lasting effect of 

 fertilizers. 4. Manure as a Fertilizer: (a) Some facts about 

 manure: (1) Fertilizing value about $2.34 per ton. (2) 

 Manures differ in fertilizing value. (3) Feeding affects 

 value of manure. (4) Amount of manure produced by farm 

 animals. (5) Liquid portion of manure valuable. (6) Some 

 practical pointers on use and care of manure: (1) Manure 

 has three-fold value. (2) Manure a quick fertilizer. (3) 

 Stall manure better than open-yard manure. (4) Hints on 

 storing manure. (5) Light applications better than heavy 

 applications. (6) Plowing under vs. discing in manure. 

 (7) Applying manure to clover fields. (8) Manure not a 

 perfect fertilizer. 



XIII. SOIL ACIDITY AND LIMING IN RELATION TO SOIL FERTILITY .... 229 

 1. Soil Acidity Explained. 2. Soil Acidity Lowers Soil 

 Fertility (Productiveness). 3. The Meaning of Liming. 



4. How Liming Improves Acid Soils: (a) Available calcium 

 is added for clover and alfalfa. (6) Absence of acidity favors 

 the helpful soil organisms, (c) Plant-food elements are 

 rendered more available, (d) Greater returns are secured 

 from fertilization, (e) Lime tends to improve tilth on 

 heavy soils. (/) Helps to control malnutrition diseases of 

 truck crops, (g) Weeds may be better controlled. 5. Crops 

 Benefited by Liming When Grown on Acid Soils. 6. Crops 

 Which Tolerate Acidity. 7. How Acid Soils May be Deter- 

 mined: (a) By the use of blue litmus paper; (6) by chemical 

 tests; (c) by alfalfa and clover failures; (d} by the growth of 

 certain plants. 8. Low Wet Lands not Necessarily Acid. 

 9. How Soils Become Acid Extent of Acid Soils. 10. The 

 Nature of Soil Acidity. 11. Kinds of Agricultural Lime. 

 12. Comparative Value of Agricultural Limes the Best to 

 Use. 13. Amount of Lime to Apply. 14. When, How and 

 How Often to Apply Lime. 15. Deep Plowing Cannot be 

 Substituted for Liming. 16. Soils Derived from Lime- 

 stone May Become Acid. 17. Soil Fertility is Regulated 

 Through Liming. 



XIV. HARMFUL AGENTS IN SOILS AFFECTING FERTILITY 255 



1. Worms and Insects in Soils May Destroy Crops. 2. 

 Diseases in Soils May Cause Crop Failures. 3. Too Much 

 Water in Soils is Harmful. 4. Alkali Salts in Soils is 

 Injurious. 5. The Toxin Theory of Infertility. 6. Other 

 Harmful Agents. 



