586 



INDEX OF SUBJECT MATTER 



Soil organic matter, amount of in 



Minnesota soils, 119. 

 amount of in soils of United States, 



117. 

 general nature, 7. 

 importance of, 121. 

 maintenance of, 122. 

 resume of, 126. 

 source and character of, 99. 

 Soil organisms, and the free-fixation of 



nitrogen, 431. 

 benefits of, 397. 

 general methods of study, 399. 

 groups of, 384. 



influence in nitrate assimilation, 426. 

 influence of alkali on, 335. 

 injurious to higher plants, 396. 

 macro-animal forms, 384. 

 macro-plant forms, 385. 

 micro-animal forms, 386. 

 micro-plant forms, 388. 

 resume of, 440. 

 Soil particles, character as determined by 



size, 69. 

 classification of, 67. 

 minerological character, 75. 

 number of, 95. 

 surface of, 97. 

 Soil separates, chemical and minerological 



characters, 75. 

 chemical composition of, 78, 79. 

 physical characters of, 73. 

 sizes of, 67. 

 specific gravity of, 89. 

 Soil solution, as studied by aqueous ex- 

 traction, 279. 

 as studied by depression of freezing 



point, 280. 

 composition data of, 283, 288. 

 concentration data of, 282, 285, 



286. 

 general character of, 275. 

 influence of crop on, 284. 

 influence of miscellaneous factors on 



286. 

 influence of season on, 283. 

 methods of study, 277. 

 qualitative composition of, 280. 

 quantitative composition of, 282. . 

 relation to absorption, 276. 

 relation to productivity, 287. 

 summary of, 288. 



Soil structure, ideal, 88. 



nature of, 87. 



types of, 139. 

 Soil temperature, control of, 244. 



data of, 243. 



influence of slope, 229. 



variations of, 242. 

 Soil water, availability of. 198. 



diagram of forms, 199. 



effect on air movement, 258. 



effect on specific heat of soils, 233. 



form of molecule, 28. 



forms of, 151. 



function to plants, 184. 



general characteristics of, 152. 



influence on plants, 186. 



loss by evaporation, 216 



loss by percolation, 206. 



loss by percolation at Cornell, 209. 



loss by percolation at Rothamsted, 

 207. 



modes of loss, 202. 



methods of expressing, 156 



run-off losses, 203. 



summary of control, 221. 



thermal movement of, 182. 

 Soluble matter carried into ocean, 46. 

 Soluble salts in soil, influence on nitri- 

 fication, 421. 

 Solubility of nutrients as influenced by 



carbon dioxide, 255. 

 Solution, loss of nutrients because of, 23. 



importance of in soil formation, 27. 



relation of to soil productivity, 28. 

 Specific gravity of minerals, 89. 

 Specific gravity of soils, defined, 88. 



determination of, 90. 

 Specific gravity of soil separates, 89. 

 Specific heat, data on soils, 232. 



defined, 231. 

 Specific heat of soil, 231. 



factors affecting, 232. 

 Stages in the decay of green manures, 



542. 

 Stassfurt salts, chlorides and sulfates, 

 463. 



kainit, 463. 



silvinit, 463. 

 Stone drains, construction of, 212. 

 Straw, influence on nitrate reduction, 



425. 

 Streams, soil formation by, 46. 



