60 CHEMISTRY OF FARM PRACTICE 



consists of the inorganic and organic materials; the liquid 

 part consists of water carrying more or less of mineral or 

 of organic materials in solution; the gaseous part consists 

 of air, mixed with carbon dioxide produced by the decom- 

 position of organic matter, water vapor and other gases. 

 The whole may be likened to an animal, the solid part 

 forming the body, the skeleton of which represents the 

 inorganic solids, while the flesh and muscles represent 

 the organic solids; the soil water and its contents con- 

 stituting the circulatory system of the animal, and the 

 air and other gases the respiratory system. 



51. Soil Water. All plant food that enters the plant 

 from the soil is transferred to the plant in solution; there- 

 fore, we see that the plant food in the soil must become 

 soluble in the soil water before the plant can use it for the 

 building of its tissues. It is a wise provision of nature 

 that the better treatment of the land accentuates the 

 factors that promote solution, while poor methods of soil 

 treatment make the plant food elements less soluble. 



The rainfall of the different sections of the United 

 States is variable, ranging from about 100 inches in the 

 most humid areas to as low as from 2 to 5 inches in the 

 most arid regions. The rainfall most desirable for maxi- 

 mum production is about 50 inches. When rainfall is 

 less, there is more reason for greater efforts toward con- 

 servation of moisture. 



There are three forms of water in the soil: Gravitational, 

 capillary, and hygroscopic. The gravitational or free water 

 moves under the force of gravity. Generally it is more 

 harmful than helpful, because it leaches soluble plant food, 

 excludes the air, hinders bacterial action, reduces surface 

 tension, and dissolves cementing materials. It is helpful 

 to the extent that it is converted into the capillary form. 

 Also it may serve to wash some harmful bodies out of 

 the soil. 



The capillary moisture is the liquid film which surrounds 



