268 ELEMENTS OF FARM PRACTICE 



IRRIGATION 



Irrigation is the application of water to land artificially. 

 In many parts of the United States there is not enough 

 rainfall to ensure crops. In other parts there is practically 

 no rainfall. In these places, if crops are to be grown, water 

 mus{ be supplied artificially. 



Sources of water for irrigation are rivers, reservoirs, 

 wells and lakes. Many rivers start up in the mountains 

 and flow down through lower and flat country. For irriga- 

 tion purposes, these rivers are dammed up, or a part of the 

 water is diverted from the main stream and carried by 

 means of ditches to the land to be irrigated. Reservoirs are 

 often constructed in some position higher than the land to 

 be irrigated. Water from snow or rain on the hills higher 

 than the reservoir is caught in the reservoir. As it is wanted, 

 it is conveyed in ditches out over the land to be irrigated. 

 Water is sometimes pumped from wells, streams or lakes, 

 and thus raised high enough so that it can be carried m 

 ditches to fields needing irrigation. Water may be pumped 

 directly into the ditches as needed, or it may be pumped 

 at any time and stored in reservoirs for use later. 



Distribution. — Watering a lawn with a hose or a flower 

 bed with a sprinkling can is irrigating, but this means of 

 applying water to the soil is naturally limited to very small 

 areas. During a crop season it is necessary to apply water 

 equal to several inches deep over the land to ensure a good 

 crop. We have learned that it requires more than 500 

 barrels to cover an acre one inch deep. To make irrigation 

 practical, some very easy way of distributing water is neces- 

 sary. The most common way of distributing water is by 

 means of open ditches. Large ditches with high banks are 

 dug through the fields to be irrigated. By damming up 

 the ditches the water can be raised in them a little higher 

 than the surrounding fields. Then small lateral ditches a 

 few feet apart may be opened at the sides of the big ditch, 

 and the water will then flow out over the land and settle 

 into the soil just as rain. In a few places water is carried 

 over the fields in tile laid just under the surface of the soil. 

 The water comes out of the joints in the tile, and is absorbed 

 by the soil. This method is called sub-irrigation. 



