CONTENTS 



PART II 



SOIL FERTILITY AS AFFECTED BY FARM OPERATIONS AND 

 FARM PRACTICES 



Chapter Page 



XVI. A FERTILE SOIL ....... 141 



Physical properties : 



Power to absorb and hold water 



Power of ventilation 



Power to absorb and hold heat . .142 

 Biological properties ..... 143 



Nitrogen-fixing germs .... 144 



Nitrifying germs ..... 145 



Denitrifying germs .... 147 

 Chemical properties : 



Nitrogen in the soil 



Phosphoric acid in the soil 



Potash in the soil 



Lime in the soil 



Great importance of physical proper- 

 ties ....... 147 



Maintenance of fertility .... 150 



XVII. SOIL WATER ....... 151 



Importance of soil water . . . .151 



Necessity of soil water . . . .151 



Sources and forms of soil water . . 153 

 Too much water ...... 154 



Not enough water ..... 154 



Loss of soil water ..... 155 



How some farm operations influence soil 

 water ........ 156 



Hoeing, raking, harrowing and cultivating 158 

 Manures and soil water .... 159 



Methods of cropping and soil water . 159 

 Selection of crops with reference to 

 soil water ...... 160 



