IRRIGATION AND DRY-FARMING 695 



with a channel that is deep in relation to its width, not 

 only reduces seepage, but also, by permitting the rapid 

 flow of water, reduces loss by evaporation. 



At the farm on which the water is to be used, it is dis- 

 tributed in small field laterals which are carried on the 

 higher ground. Precautions against seepage and evapo- 

 ration should here be taken. The tendency now is toward 

 the distribution of the water to the fields by means 

 of underground oipes, with standpipes and valves at 

 the points of discharge. The arrangement of the farm 

 laterals must of course be determined by the topography 

 of the land, since the water flows by gravity. 



597. Preparation of land for irrigation. — The prep- 

 aration of the land for irrigation depends on the method 

 used to apply the water. Usually marked irregularities 

 should be removed by smoothing the surface. Where 

 any sort of basin method of irrigation is used, it may also 

 be necessary to level the surface. Various types of scrap- 

 ers and levelers have been found useful for this operation. 

 Much of the arid and semiarid land carries a growth of 

 sage brush or other bushy vegetation, and of course 

 this must be removed before smoothing operations can 

 become effective. 



598. Methods of applying water. — There are four 

 general methods * of applying water to the soil. These 

 are (1) overhead sprays, (2) sub-irrigation, (3) flooding, 

 and (4) furrows. 



599. Overhead sprays. — By the overhead spray system 

 (Fig. 76) the water is distributed in pipes under a pres- 

 sure of forty to sixty pounds and discharged from a series 



1 Fortier, S. Methods of Applying Water to Crops. U. S. 

 D. A,, Yearbook 1909, pp. 293-308. 



