288 Ground Water, Wells and Farm Drainage. 



Proper drainage so lowers the ground water surface that 

 roots are able to penetrate to their normal depth, and Fig. 

 Ill shows how the roots of corn have been massed together 

 near the surface because of too much water in the soil be- 

 low, and Fig. 45, p. 147, shows the apparatus with the corn 

 growing in it. 



358. Drainage Increases the Available Moisture. When 

 the roots of a crop are forced to develop so close to the sur- 

 face as shown in (357) the first effect is to exhaust the soil 

 of its moisture so much as to leave it too dry and so lessen 

 the capillary rise that, although there is an abundance of 

 water in the soil below, it cannot be brought to. the roots 

 and the soil below is too wet to permit the roots to go to 

 the moistura 



On the other hand if the ground water is lowered the 

 roots are permitted to advance deeper, making it unneces- 

 sary for the water to move up as high and leaving the soil 

 more moist, and so capillary action stronger and capable of 

 lifting water higher and faster. (198.) (199.) 



359. Soil Made Warmer by Drainage. Whenever soils 

 are kept continuously wet, so that large amounts of water 

 evaporate from their surfaces, the temperature is low. Two 

 thermometers having their bulbs side by side, one left naked 

 and the other covered with a close fitting layer of wet mus- 

 lin, will often show tempera-toes as much as 20 different, 

 the wet one colder, made so by the evaporation of water. 

 The teakettle on the stove has the temperature of its bottom 

 held constantly near 212 by the evaporation of the boil- 

 ing water, showing the cooling power of water when evapo- 

 rating. 



During early spring differences in soil temperature at the 

 surface, due to differences in drainage, may often be as 

 great as 12. 



The differences in the amount of moisture in clayey and 

 sandy soil often cause a difference of 7 F., in the surface 



