Water and Watering 37 



likely to be an over-supply of moisture, and at another 

 part of the year the rainfall is likely to be deficient. The 

 irrigation plant, of whatever type, becomes extremely 

 useful during the dry part of the year. Many of the vege- 

 tables not now grown in these regions will thrive 

 luxuriantly if only a sufficient and constant water supply 

 is at hand. (See Plate I.) 



Over-head irrigation. 



Under the general head of over-head irrigation are in- 

 cluded all kinds of irrigation in which nozzles, pipes, and 

 other appliances are used for distributing water above the 

 surface of the ground. This is not an economical way to 

 use the water, and a considerable quantity is lost by evap- 

 oration, since the particles are thrown into the atmosphere 

 in the form of drops of water, and in a windy time much of 

 the moisture is carried away. It has an advantage over 

 the other systems of irrigation in that it is applicable to 

 any kind of soil, no matter whether the surface is uneven or 

 broken. An almost endless variety of nozzles for distribut- 

 ing water by this system may be secured and the varia- 

 tions are as extensive as the ingenuity of the vegetable- 

 growers. 



One essential part of such a plant is the central tank, 

 placed on a tower or elevation of about 60 feet above the 

 field to be irrigated. This gives sufficient pressure to 

 operate the nozzles that are designed for this purpose, or 

 approximately 30 pounds pressure. The size of the tank 

 for holding the water will be determined by the area of 

 the land to be irrigated at one time. The main object of 

 the elevation of the water is to give uniform pressure. 



