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 properties 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

XVIII.--THE AFTER-CULTIVATION OF CROPS 164
Loss of water by evaporation 164
Loss of water through weeds 165
Saving the water 165
Time to cultivate 166
Tools for after-cultivation 167
Hilling and ridging 169

XIX.--FARM MANURES 171
The functions of manures and fertilizers 171
Classification 171
Importance of farm manures 172
Barn or stable manure 173
Loss of value 173
Checking the losses 176
Applying the manure to the soil 177
Proper condition of manure when