Chapter IV: Nitrification

Process of nitrification 161
Occurrence of nitrates in the soil 162
Nitre soils of India 162
Saltpetre plantations 163
Cause of nitrification 165
Ferments effecting nitrification 167
Appearance of nitrous organisms 168
Nitric organism 169
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 denitrification 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

APPENDIX TO CHAPTER IV.
NOTE
I. Old theories of nitrification 196
II. Nitrification takes place in solutions devoid of organic
matter 196
III. Oxidising power of micro-organisms in soils 197
IV. Effect of urine on nitrification in soils 197
V. Solution used by Professor Frankland in cultivating
nitrificative micro-organisms 198
VI. Experiments by Boussingault on rate of nitrification 198
VII. Nitrogen as nitrates in Rothamsted soils after bare
fallow in lb. per acre 198