vi CONTENTS 



tion of air and gases ; Action of vegetation and micro-organisms ; 

 Distribution of soils ; Sedentary and transported soils ; Rocks 

 and minerals from which soils are derived as quartz, feldspar, mica, 

 hornblende, zeolites, granite, apatite, kaolin, limestone, gypsum ; 

 Chemical composition of rocks. Pages 49-59. 



CHAPTER III 



Chemical Composition of Soils. — Elements combine to form 

 minerals ; Classification of elements ; Combination of elements ; 

 Forms in which elements are present in soils ; Acid-forming ele- 

 ments, silicon, double silicates, carbon, sulphur, chlorine, phos- 

 phorus, nitrogen, oxygen, hydrogen ; Base-forming elements, alu- 

 minum, potassium, calcium, magnesium, sodium, iron ; Classifica- 

 tion of elements for plant-food purposes ; Amount of plant food in 

 different forms in various types of soils ; How a soil analysis is 

 made ; Value of soil analysis ; Interpretation of the results of soil 

 analvsis ; Use of dilute acids as solvents in soil analysis; Distribu- 

 tion of plant food in the soil ; Composition of typical soils ; 

 "Alkali" soils and their improvement; Organic compounds 

 of soil ; Sources ; Classification ; Humus ; Humates ; Humification ; 

 Humates produced by different kinds of organic matter ; Value 

 of humates as plant food, amount of plant food in humic forms ; 

 Loss of humus by forest fires, by prairie fires, by cultivation ; 

 Humic acid ; Soils in need of humus ; Soils not in need of humus ; 

 Composition of humus from old and new soils ; Influence of different 

 methods of farming upon humus. Pages 60-101. 



CHAPTER IV 



Nitrogen of the Soil and Air, Nitrification and Nitrogenous Ma- 

 nures. — Importance of nitrogen as plant food ; Atmospheric 

 nitrogen as a source of plant food. Experiments of Boussingault, 

 Yille, and Lawes and Gilbert ; Result of field trials ; Experiments 

 of Hellriegel and Wilfarth and recent investigators ; Composition 

 of root nodules ; Amount of nitrogen returned to soil by leguminous 

 crops and importance to agriculture ; Nitrogenous compounds 

 of the soil ; Origin ; Organic nitrogen ; Amount of nitrogen in soils ; 

 Removed in crops ; Nitrates and nitrites ; Ammonium compounds ; 



