Contents. v 



CHAPTER XL 



CHEMICAL AND MINERAL NATURE OF SOILS. 



PAGTB. 



ESSENTIAL CONSTITUENTS OP A FERTILE SOIL 69 



FUNCTIONS OF ESSENTIAL PLANT FOODS 70 



CHEMICAL COMPOSITION OF SOILS 71 



Difference between clayey and sandy, p. 71 ; Differences due to 

 texture, p. 72 ; Between soils and subsoils, p. 72 ; Between clay 

 and humus, p. 73 ; Between clay and loess, p. 73 ; Between 

 arid and humid, p. 73 ; between soil and rock, p. 77. 



HUMUS , 76 



Of arid and humid climates, p. 76. 



PLANT FOOD 79 



Amount removed from soil by crops, p. 79 ; Amount in soil, p. 79 ; 

 Number of crops prodaced, p. 80 ; Rothamstead experiments, 

 p. 81. 



NITROGEN IN THE SOIL 82 



Amount in Manitoba soils, p. 82 ; Forms of occurrence, p. 83 ; Dis- 

 tribution in soil, p. 83 ; Amount as nitric acid, p. 84. 



SOURCES OF SOIL NITROGEN. . 85 



Of humic nitrogen, p. 85; Symbiosis, p. 87; Observations of Wino- 

 gradsky and Berthelot, p. 88. 



NITRIFICATION" 89 



DBNITUIFICATION 89 



CHAPTER III. 



SOLUBLE SALTS IN FIELD SOILS. 



SOLUBLE SALTS IN FIELD SOILS 92 



Amount, p. 92 ; Amount limiting plant growth, p. 93 ; Mode of 

 action on plants, p. 93 ; Concentration in Zones, p. 94 ; Origin, 

 p. 94 ; In marsh soils, p. 95. . 



LEACHING NECESSARY TO FERTILE SOILS 95 



Correction of alkali lands, p. 95 ; Drainage ultimate remedy, p. 98 ; 

 Tillage helpful, p. 98. 



CHANGES IN AMOUNT OF SOLUBLE SALTS : 98 



With season, p. 98 ; with different crops, p. 99. 



NITRATES 101 



Relation to total salts, p. 101 ; Closeness of plant feeding, p. 101 ; 

 Limits at which, plants turn yellow, p. 102; In fallow and 

 cropped ground, p. 103 ; Loss during winter, p. 104 ; Influenced 

 by cultivation, p. 105. 



PHYSICAL EFFECTS OF SOLUBLE SALTS 106 



On movements of soil moisture, p. 106 ; On surface tension, p. 106 ; 

 On evaporation, p. 10G ; On viscosity, p. 106. 



