INDEX 



257 



Nodules on roots of legumes, 114—117 

 Non-symbiotic nitrogen-fixing bac- 

 teria, 104-113 

 Nucleic acids, decomposition of, 173 

 Numbers of microbes in soil, 46—47, 



48, 52, 56-58 

 Nutrients, absorption of, by plants, 17 

 Nutrition, of microbes, 25-27 

 of plants, 14-19 



O 



Occurrence of microbes in soil, 23, 



44-45, 46-48 

 Olivine, weathering of, 4 

 Organic acids in soil, 163 



production of, by microbes, 156- 

 157 

 Organic compounds, absorption of, 

 by plants, 194-195 

 kinds of, added to soil, 76 

 Organic materials, simplification of, 



75 

 Organic matter, composition of, 78, 79 

 decomposition of, by microbes, 14, 

 75-101, 204-216 

 influence of, on microbial activ- 

 ities, 204-216 

 on nitrification, 143, 146 

 on soil microbes, 60-61, 83-85, 



87, 92, 204-216, 219 

 on soil nitrogen, 92-101 

 mechanism of, 94—99 

 effects of microbes on, 244—245 

 insoU, 8, 9, 11-12, 16 

 loss of, during decomposition, 98- 



101 

 nitrogenous, decomposition of, 126- 



135 

 soil, carbon-nitrogen ratio of, 99- 

 101 

 Organic substances, influence of, on 

 physical condition of soil, 

 195 

 Orthoclase, weathering of, 4 

 Oxalic acid, 163 



Oxygen, influence of, on nitrification, 

 137-139, 142-143 



Parasitic nature of microbes, 22, 45 

 Parasitic nematodes, 41 

 Partial sterilization, 224-229 

 influence of, on nitrif3dng bacteria, 

 138-139 

 on soil microbes, 224-229 

 on soils, 224-228 

 Peat, formation of, 154-155 

 Peat soils, 12 

 Pecto-celluloses, 82 

 Pedolog}', science of, 1 

 Penicilliuni, 30, 33 

 Pentosans, decomposition of, 81 

 Phoma, fLxation of nitrogen by, 106 

 Phosphate, reduction of, 172-173 

 Phosphates, influence of, on soil 



microbes, 222-223 

 Phosphoric acid in soil, 16, 18 

 Phosphorus, action of microbes on, 

 249 

 influence of, on cellulose decompo- 

 sition, 84-85 

 on nitrogen fixation, 113 

 in plant nutrition, 14, 15-16 

 in soil, 173 



soil, availabihty of, determined by 

 nitrogen-fixing bacteria, 113 

 transformation of, by microbes, 

 173-176 

 Phosphorus availability, Aspergillus 

 niger method, 238 

 Azotobacter methods, 238-239 

 Phycomycetes, 33 

 Physical properties of soil, 10 

 Physical structure of soil, 12-13 

 Physiological methods for studying 



microbes, 48 

 Phytic acid, decomposition of, 173 

 Plant, decomposition of, as a whole, 



91-94, 97-101, 146 

 Plant constituents, most important, 



77-78 

 Plant growth, importance of microbes 

 to, 242-243 

 influence of decomposition of or- 

 ganic matter on, 93 



