CHAPTER XIX 

 IRRIGATION CULTURE 



The Amount of Water Required for Crops. As explained 

 in the part of the text devoted to drainage, nature does not 

 in all cases supply the amount of water which will produce the 

 maximum growth of plants. In this connection the question 

 of the amount of water which, when properly applied, will 

 produce a paying yield of crops, is one of vast importance 

 to those interested in irrigation. In most instances irriga- 

 tion water is expensive, and for the sake of economy no more 

 water should be used than necessary. The question, how- 

 ever, is very complex, and cannot be treated otherwise than 

 very briefly in this text. 



The water which comes to the soil leaves it in three dif- 

 ferent ways: First, a portion of it is transpired through 

 plants; second, a portion evaporates from the surface of the 

 soil; third, a certain amount of the water flows away over the 

 surface or as underground drainage. Plants grow by using 

 water, as described under the first head. The other two 

 ways in which the water leaves the soil may be considered 

 losses, and should be reduced to the minimum. 



There are many conditions which modify the amount of 

 water required for irrigation. These may be enumerated as 

 follows. 



The Nature of the Crop Grown. Some crops transpire 

 more than others, because they have more foliage to give 

 off the moisture. The root growth of the plant is a factor in 

 determining the amount of moisture used, as the roots of some 



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