INDEX. 



Nitrification and denitrification ........ . .............................. 145 



in alkali lands ......... ................................. 68 



in soil of " ten-acre tract. " ............................... 359 



intensity in arid climates, ................................ 68 



list of substances favoring ................................ 147 



of organic matter in soils, experiments .................. 358 



not active in unhumified matter ...................... 359, 360 



Nitrifying Bacteria ................................................ 146 



Nitrobacterium ; conditions of activity .......... . ..................... 146 



Nitrogen-absorbing bacteria ........................................ 156 



Nitrogen, absorbed more abundantly than oxygen .................... 278 



accumulation of, in humus ................................. 124 



adequacy in humus, lowest limit of ........................ 363 



in soils ........................................ 357 



availability of, in soils ; ascertainable ....................... 363 



content of humus .......................................... 135 



deficiency, pot test, figure .................................. 362 



determination of, in soils ............................ .... 357 



hungry soils ; table ....................................... 361 



percentages in humus, what are adequate .............. ... 360 



supply of plants, views on .................................. 150 



Nitrosomonas, figure ....................... . ............... .......... 246 



Nodules of legumes ................................................ . 151 



North Central States, herbaceous vegetation on calcareous soils ... .514, 515 



lowland growth in uplands, when ......... , ...... 515 



vegetation and soil-character .................... 513 



Nutritive salts in alkali ............................................. 441 



O. 



Ocean currents, Gulf -stream and Japan-stream 295 296 



Olive, resistance to alkali 47^ 



Organic and organized constituents of soils 120 



Organisms influencing soil-conditions 142 



Oxalic acid, secretion by lichens 19 



Oxidation, expansion by 18 



Oxids constituting earth's crust ; table 31 



Oxygen, action in weathering rocks 18 



proportion of, in earth's crust 3 



P. 



Pamperos 9 



Peat bogs * 22 



Peaty soil, shrinkage II 7 



Percolation in natural soils : diagram 22 3> 22 5i 22 ^ 



rate of, as influenced by grain-sizes 224 



Permanent value of land vs. Immediate productiveness 34 



