CHAPTER XIII 



IRRIGATION 



Definition. Irrigation is the artificial application of water 

 to land for the purpose of promoting vegetable growth. 

 While generally thought to have been developed in modern 

 times, it was practiced in Egypt from 2000 to 1000 B.C. It 

 has been employed in this country as an adjunct to agricul- 

 ture for about seventy years and has been extensively devel- 

 oped in the past thirty years. Until recently irrigation has 

 been limited generally to the arid and semiarid regions, but it 

 has been found beneficial to certain classes of crops in the 

 humid regions, and each year witnesses an increased develop- 

 ment among gardeners and fruit growers. In fact, its 

 application where rainfall is heavy is more general than 

 might be supposed on first thought. In the western states 

 any sprinkling or watering of plants is considered irrigation, 

 but in the eastern part of the country it is not the custom so 

 to designate the watering of gardens and lawns with pails, 

 hose, and various mechanical sprinklers. 



Importance of water. Water is essential for plant growth. 

 It is taken in through the roots, circulates through the plant 

 vessels, and is evaporated from the leaves or built into tissue. 

 It serves three purposes: first, as a direct food for the plant 

 either as water contained in the soil or by breaking up into 

 hydrogen and oxygen and being used in new compounds; 

 second, as a transporting medium which carries food from 

 the soil and air to the point of assimilation in the plant; 

 third, as a regulator of the physical condition of the plant. 

 The quantity of water used by a crop is very large, from 200 

 to 500 pounds being necessary for the production of 1 pound 

 of dry matter. From 60 to 90 per cent of the weight of all 

 staple crops is due to water. When there is not sufficient 



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