xii CONTENTS 



CHAPTER XXI. 



NITRIFICATION 



Early Theories 208 



The Dawn of the Biological Theory . 209 



Isolation of Nitrifying Ferments 211 



Distribution . . 217 



Reaction of Media 218 



Food Requirements of Nitrifiers . 220 



Organic Matter . 222 



Energy 223 



Metabolism 223 



Morphology . 225 



Influence of .Moisture 226 



Temperature 230 



Light Rays 230 



Aeration and Cultivation 230 



Crop and Fallow 231 



Season 234 



Quantity of Nitrates Formed 235 



Loss of Nitrates 236 



References 238 



CHAPTER XXII. 



DENTRIFICATION 



Early Theories 239 



Organisms Concerned 240 



Reaction of the Media 241 



Food Requirements 242 



Metabolism of Denitrifying Organisms 243 



Influence of Water 244 



Temperature 245 



Losses of Nitrates from Manure and Soil 245 



Function of Denitrifiers 247 



References 247 



CHAPTER XXIII. 



AZOFICATION 



Historical 248 



Distribution 252 



Reaction of the Media 254 



Food Requirements of the Azofiers 256 



Organic Soil Constituents 259 



Influence of Colloids 260 



Sources of Energy for the Azobacter 261 



Manure . . 266 



Metabolism of Azotobacter 267 



Pigments Produced by Azotobacter 270 



Morphology of the Nitrogen-fixing Organisms 271 



Methods .272 



Relation of Azotobacter to Other Organisms 274 



The Influence of Water 276 



Temperature .... 278 



Light and Other Rays ' 281 



Aeration 281 



Season 281 



Crop 282 



Climate . . 283 



Relationship of Azotobacter to Nitrate Accumulations .... 284 



Soil Inoculation . 284 



Soil Gains in Nitrogen 287 



Reference 289 



