90 SOIL WATER AND ITS RELATION TO SOIL FERTILITY 



production of a seventy-five-bushel yield for each twenty-three-foot 

 square area, the area necessary to grow one bushel must furnish 

 to the corn growing on it at least 152 barrels of water during the 

 growing season, or an equivalent of about thirteen inches. All 

 this water passes up through the plants and evaporates from the 

 leaves. This current of water passing up through the plant and 

 evaporating from the leaves is called the " transpiration current." 

 Approximately 140 barrels of water are transpired by the oat 



Fia. 37. One hundred fifty-two barrels of water are required to produce one 

 bushel of corn. The corn uses this amount of water. Water is an important factor in crop 

 production. 



plants for each bushel of oats produced. The same amount is 

 required per bushel of barley. In a similar manner about 3800 

 barrels are required to grow a ton of clover hay, and about 4200 

 barrels to produce a ton of alfalfa hay. 



" Water Requirement " of Plants. The expression "water 

 requirement" of a plant refers to its needs and means the amount 

 of water that passes up through it and evaporates for every pound 

 of dry matter produced. Plants differ in their water require- 

 ments, and, for the same plant, climate influences this require- 

 ment considerably. In this country scientists have found the 

 water requirement of some crops to be as shown in the following 

 table: 



