436 



INDEX 



Rainfall, storing of, in dry farming, 



247 

 types of, over dry-land area of 



United States, 239 

 Reaction, alkaline, of soil desirable 



for bacteria, 320 



Reade, rate of lowering of land sur- 

 face by solution, 24 

 Real or absolute specific gravity, 175 

 Reclamation of alkali lands, chap- 

 ter on, 278 

 Redding, R. J., depth of plowing for 



cotton on eroded land, 364 

 Reforesting stops erosion, 369 

 Reservoirs, storing water for irriga- 

 tion, 259 

 Residual soils, 27 

 Residues, organic, 17D 



return of, aid in preventing ero- 

 sion, 363 



Resurrected forest, 55 

 Rhyolite, 7' 

 River Flood Plains province, 97 



sediments, composition of, 262 

 swamps, 28 



water, suspended matter in, 262 

 Rock disintegration and talus slope, 



32 



outcrop, 116 

 phosphate, 400 

 split by tree, 19 

 weathering of jointed, 31 

 Rocks, 6 



aqueous, 7 



decomposition and disintegra- 

 tion of, 1 1 

 eruptive, 6 



expansion of, on heating, 13 

 igneous, 6 

 intrusive, 6 



loss of constituents through de- 

 composition, 22 

 metamorphic, 10 

 plutonic, 6 

 volcanic, 6 



weathering of, chapter on, 11 

 Rocky Mountain and Plateau Re- 

 gion, 104 

 Rodents, mix surface and subsoil, 



315 

 Rogers Brothers, dissolved minerals 



in carbonated water, 22 

 Rollers, 335 to 337 

 Roosevelt dam, 260 

 Root injury, 353 



pruning of corn, results, 355 



Root systems, depth of, varied in ro- 

 tations, 378 



Roots and tops, legumes, compo- 

 sition of, 398 

 force exerted by, 19 

 in Chernozem soils, 144 

 of plants aid percolation, 220 



tree prying rock apart, 19 

 Rotation, chapter on, 376 



advantages of, better distribu- 

 tion of work, 377 

 control of insects and plant 



diseases, 377 

 of weeds, 377 

 compared with continuous corn, 



Iowa, 379 

 effect of, on crop yields, Illinois, 



Ohio, Minnesota, 379, 380 

 for corn and winter wheat belt, 



382 



cotton belt, 384 

 spring wheat belt, 386 

 helps maintain good tilth, 378 



organic matter, 378 

 produces larger yields, 378 

 renders toxic substances less 



harmful, 378 

 variation in depth of root 



systems, 378 



of crops, aid in maintaining or- 

 ganic matter, 171 

 place for crops in, 381 

 planning of, 380 

 Rotmistrov, weeds enemy of culture, 



friends of drought, 244 

 water not raised far by capil- 

 larity at Odessa, 210 

 Run-off, cause of loss in dry farm- 

 ing, 242 

 Russell, origin of adobe, 65 



Sage brush on land well adapted to 



dry farming, 239 

 Salts, soluble, in soils, 74 

 Sampling of soils, 120 

 tube, King's, 119 

 Sand dune, bun-ing forest, 55 



wind ripples on, 56 

 dunes, migratory or wandering, 



54, 58 



permanent or fixed, 54, 55 

 held by, black locusts, 59 

 bunch grass. 60 

 partridge pea, 59 

 pines, 60 

 sensitive plant, 59 



