XVI CONTENTS. 



Difficulty in isolating them 169 



Nitrifying organisms do not require organic matter . .169 



Conditions favourable for nitrification 



Presence of food-constituents . . . . . .170 



Presence of a salifiable base . . . . . .171 



Only takes place in slightly alkaline solutions . . .172 



Action of gypsum on nitrification 173 



Presence of oxygen 173 



Temperature . . . . . . . . .175 



Presence of a sufficient quantity of moisture . . .176 

 Absence of strong sunlight . . . . . .176 



Nitrifying organisms destroyed by poisons . . .176 



Denitrification . .177 



Denitrification also effected by bacteria . . . .178 

 Conditions favourable for den itrifi cation . . . .178 

 Takes place in water-logged soils 179 



Distribution of the nitrifying organisms in the soil . . .179 

 Depth down at which they occur . . . . .180 

 Action of plant-roots in promoting nitrification . . .181 

 Nature of substances capable of nitrification . . .181 



Rate at which nitrification takes place . . . . .183 



Nitrification takes place chiefly during summer . . 183 



Process goes on most quickly in fallow fields . . .184 

 Laboratory experiments on rate of nitrification . . .185 

 Certain portions of soil - nitrogen more easily nitrifiable 

 than the rest ........ 187 



Rate of nitrification deduced from field experiments . .187 

 Quantity of nitrates formed in the soils of fallow fields . 188 

 Position of nitrates depends on season .... 188 



Nitrates in drainage- waters . . . . . .188 



Amount produced at different times of year . . .189 

 Nitrification of manures . . . . . . .190 



Ammonia salts most easily nitrifiable . . . .191 



Sulphate of ammonia the most easily nitrifiable manure . 191 

 Rate of 'nitrification of other manures . . . .192 



Soils best suited for nitrification . . . . .192 



Absence of nitrification in forest-soils . . . .193 



Important bearing of nitrification on agricultural practice . 193 

 Desirable to have soil covered with vegetation . . .194 

 Permanent pasture most economical condition of soil . 194 

 Nitrification and rotation of crops 195 



