398 



INDEX 



Timothy, not a soil robber, 65 



where grown, 275 

 Tobacco, a heavy feeder, 63, 64, 199, 203 



phosphorus lost in growing, 267 



response to liming, 233 



rotations for, 276, 278, 280 



stems as fertilizers, 202, 203 



where grown, 277 

 Toxin theory of infertility, 261 

 Transported soils, 15 

 Tropical soils, 45 

 Truck crops and liming, 233 

 rotations for, 280 

 where grown, 281 

 True clay, denned, 41 

 Truog test for acidity, 234 

 Turnips, as feeders, 63, 67 



for clay soils, 325 



Unferilized plot, value of, 370 



Vegetative period, defined, 49 



activities in, 50 



conditions and requirements, 50, 51 

 Velvet bean, for green manure, 193 



for sands, 310, 312, 316 



for soil improvement, 310 

 Vertical drainage, defined, 113, 124, 126 



forms of, 124, 126 

 Vetch, for green manuring, 193 

 for sands, 316 

 rotations for, 280 



Waste lime, 243 

 Water, a part of soil medium, 12 

 amount crops require, 89, 90 

 soils give up, 91 

 held by peat, 94 



by soils, 93, 98 

 available water in soils, 98 

 capillary, defined, 93 

 conservation and control, 100 

 forms of, in soil, 93 

 free, defined, 93 

 gravitational, defined, 93 

 hygroscopic, defined, 93 

 laboratory exercises on soil, 105, 106, 



133, 185 



limiting factor in dry farming, 92 

 limits yields in humid regions, 92 

 movements of soil, 94 

 percolation of, 95 



Water problems in farming, 92 



required for germination, 49 



required by plants, 89 



too much is harmful, 109, 258, 260 



why crops require, 89 

 Water-holding capacity of soils, 98, 99 

 how to increase, 102 

 laboratory exercises on, 107 

 Watermelon, response to lime, 233 

 Water requirement of plants, 90 



factors influencing, 91 

 Water-table, defined, 113 

 Weathering, defined, 6, 172 



agents, 6, 7 



continues indefinitely, 9 



products of rock, 41 

 Weed problem on marsh soils, 301 

 Weeders, defined, 168 



illustrated, 168, 315 



light harrows for, 168 

 Weeds, as moisture robbers, 104 



controlled by liming, 230 



controlled by clover, 78 



exercises on, 87 



field studies on, 107 



for green manure, 195 



how to kill, 164, 166 



killed by shading, 78 

 Weight of soils, 71 

 Wheat, elements removed by, 63 



production on decline, 1 



rotation for, 275-277 



where grown, 276, 277 

 White alkali, defined, 44 



grubs, 255 

 Wind, a transporting agent, 15, 22 



a weathering agent, 6 



breaks in sand farming, 314 

 Winter wheat, rotations for, 267, 279 



where grown, 276 

 Wire worm, 255 

 Wood ashes, as fertilizer, 202, 203 



for acid peats, 204 



for marsh soils, 301 



for mixed fertilizers, 211 



Yeast plants, illustrated, 171 

 Yield, affected by temperature, 51 



relation to cost expense, 369 

 to profits, 369 



relatively low, 2 



