xvi CONTENTS 



Page 



1, Nitrogen Fixation 235 



Ammonium Formation (Ammonification) 236 



Nitrate Formation (Nitrification) 237 



Nitrification Capacity 237 



Nitrate Test with Diphenylamine 238 



Nitrophilous Plant Communities 239 



Denitrification 241 



2. Organisms of Weathering and Soil Formation 242 



Biogenic Weathering of Rocks 242 



Humification 242 



Putrefaction 243 



Decay 243 



Humus and Humus Formation 244 



Plant Waste: Litter 245 



Formation and Destruction of Humus 245 



Humus and Total Nitrogen 248 



Forms of Humus 248 



Adsorptively Saturated and Unsaturated Humus 249 



Varieties of Adsorptively Unsaturated Humus 250 



Moor Peat 251 



Raw Humus 251 



Alpine Humus 251 



Mull and Duff 252 



Humus Determination 252 



Degree of Humification 252 



CHAPTER IX 



Soil Tvpes 254 



Mineral Weathering 254 



Soil Climax 255 



Climatic Classification of Soils 256 



CHAPTER X 



Orographic Factors 261 



Altitude 261 



Plateaus 262 



Exposure 263 



Slopes of the Soil 268 



CHAPTER XI 



BiOTic Factors 271 



1. Fauna 271 



Pasturing 271 



2. Man 278 



Fire 278 



Effect of Fire upon Succession 279 



Cutting 283 



Mowing, Fertilization, Irrigation, Reclamation 284 



