CHAPTER 7 



Soil Water, Its Functions and Control 



Water is the most abundant substance in nature. It is necessary 

 to all forms of life. An abundant supply of moisture in the soil at all 

 seasons of the plant's growth is essential to a bountiful harvest. Sixty 

 to ninety per cent of all green plants consist of water. About forty per 

 cent of the dry matter is made from water which unites with carbon to 

 form the structure of the plant. Water is the necessary vehicle which 



Map Showing Mean Annual Rainfall for all Parts of the United States. 1 



carries plant food to the plant, and causes it to circulate from one por- 

 tion of the plant to another. When there is a deficiency of water in the 

 soil, plant growth is checked. If the deficiency becomes sufficiently 

 marked, plant growth ceases entirely. 



Amount and Distribution of Rain. — All water comes from rains and 

 melting snows. An acre inch of rain makes 113 tons of water. To 

 supply the equivalent of one inch of rainfall by artificial means at 10 

 cents per ton of water would cost $11.30 per acre. Ten inches of rain- 



1 Courtesy of Doublcday, Page & Co., Garden City, N. Y. From "Soils," by Fletcher. 



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