SOIL WATER 81 



kinds of soil are completely dried in an oven, 

 and water is then aclded to them, it will be 

 found that they will hold about the following 

 amounts : 



Sharp sand 25% 



Clay soil (60% clay) 40% 



Heavy clay (80% clay) 81% 



Loam 51% 



Garden mould 89% 



Humus 181% 



The same soils do not hold as much water as 

 this in the field, because a large part of it drains 

 off, as it must in order to make the soil congenial 

 for plants. It is far more important to know how 

 much water a soil will hold under its natural con- 

 ditions in the field, after the excess water that fills 

 the spaces has drained away and only film moisture 

 remains. The amount of film water held by dif- 

 ferent soils is about as follows: A coarse sand 

 holds but 12 to 15 per cent, by weight of film 

 moisture; a sandy loam from 20 to 30 per cent.; 

 a clay loam from 30 to 40 per cent. ; a heavy clay, 

 or a soil very rich in humus, may hold 40 to 50 per 

 cent, of film moisture. This means that a mellow 

 loam with a retentive subsoil holds four to five 

 inches of water in the first foot of soil. 



Although a sandy soil holds less water than a 

 clayey soil this disadvantage is partially offset 

 by the fact that the lighter soils give up to the 

 plants a larger percentage of the water they do 

 contain than the heavier and wetter soils. A 

 light soil may hold 30 per cent, of water and a heavy 

 soil 55 per cent., yet the lighter soil may give nearly 

 three-fourths of its water to the crop while the 

 plants could secure scarcely one-half of the water 

 held by the heavy soil. 



