INDEX 



435 



Plant diseases controlled by rota- 

 tion, 377 



food, crop requirements, 390 

 elements of, 390 

 in crops, 3!)0 



in Illinois soils, surface, 394 

 subsoil, 390 

 subsurface, 395 

 in Missouri soils, 392 

 in residual soils, 392 

 in Russian soils, 392 

 locked up in mulches, 230 

 supply in soils, 391 

 Planting seed accompanied by some 



tillage, 326 

 Plants, amount of water required 



by, 187 



disintegration by, 19 

 effect of alkali on, 282 



on rocks. 24 

 remains benefit soil, 310 

 water requirements, 241 

 Plasticity of clays, 135 

 Plow, an early form of, 340 

 pan or sole. 70 

 theoretical action of. 327 

 Plowing. 340 



deep, and turning under alkali. 



280 



contour, aid in checking ero- 

 sion, 304 

 tilling. 345 

 depth of. 344 

 fall, desirable in dry farming. 



246 



good, essentials of, 341 

 sod well turned, 341 

 poor, crooked furrow, 342 

 subsoiling, 345 

 time of, 342 

 fall, 343 

 spring, 344 



yields of wheat for different 

 depths of. in dry farming, 245 

 Plows, deep tilling double disk, 331 

 disk. 329 



general purpose, 328 

 lister. 332 

 sod. 329 

 stubble. 328 

 subsoil, 332 

 Plutonic rocks, 



Pore space, amount of in soils. ISO 

 Porosity, different grades of sand, 



183 

 of soils, 182 



Porosity of soils, of varied physical 



composition, 184 

 Potassium, 403 



effect of, on corn on swamp 



land, 404 



in fertili/.ing materials, 405 

 Potatoes, on dry farm, 253 

 Pott, 11. E., relative conductivity 



of soil material, 300 

 Prairie areas of United States, 70 



soils, 70 



Precipitates, chemical, 8 

 Precipitation, map of United States, 



190 



on earth's surface, 189 

 source of soil heat, 294 

 Preparation of seed l>ed, 345 

 Press drill, 337 

 Pressure, atmospheric, changes in, 



factor in ai : ration, 311 

 of waves. 18 

 Prestwich, lime carbonate carried 



by Thames River. 23 

 Prevention of loss of manure. 103 

 Properties, physical, of soils, chap- 

 ter on, 17.") 

 Puddling of clays, 136 



prevented by organic matter. 150 

 Pulverixing and loosening soil, an 



object of tillage, 325 

 Pumping water for irrigation, 259 

 Pyroxene. 3 



Quaking bog. 28 

 Quart/, 2 



Radiation, factor in loss of soil heat, 



295 



from sun. source of soil heat, 293 

 of heat, effect of, on soil tem 



peraturc. 302 



ratio, different colored soils, 295 

 Rainfall, affecting transpiration. 18!) 

 and evaporation from free-water 

 surface. 241 



Rothnmsted. 211 

 and snow. precipitation on 



earth's surface. 189 

 character of. effect on erosion. 



359 

 factor in value of region for 



dry farming, 238 

 map of United States. 190 

 percolation, evaporation. Roth- 



amsted, 220 



