Drainage Increases Available Moisture 423 



to the ground water supply, but not so many roots 

 are forced to take the moisture near the surface, and 

 hence for this reason capillarity is better able to hold 

 the water content up to the saturation needed. 



With the soil near the surface moist, where nitrates 

 are mostly formed, a better supply of these is kept 

 up, while at the same time there is moisture enough 

 to hold them in solution and to enable the roots 

 to obtain them. When other roots are deeper in the 

 ground, these may chiefly draw water to meet the 

 necessary evaporation w r hich goes on in the leaves, 

 and thus reserve the surface moisture for developing 

 plant -food and giving it to the plant. In this way 

 it happens that crops suffer less in times of drought 

 on well -drained, heavy soils than they do on the same 

 soils not drained. 



SOIL MADE WARMER BY DRAINAGE 



There is no cause so effective in maintaining a low 

 temperature of the soil rn the spring as the water 

 which it contains, and which may be evaporating from 

 its surface. One reason for this influence is found 

 in the fact that more heat is required to change the 

 temperature of a pound of water one degree than the 

 same weight of almost any other substance. Thus, 

 while 100 units of heat must be used to warm 100 

 pounds of water from 32 F. to 33 F., only 19.09 

 units are required to raise the temperature of the 

 same weight of dry sand, and 22.43 units an equal 

 weight of pure clay through the same range of 



