1918] EUEAL ENGINEERING. 185 



The general conclusion is drawn that in the Imperial Valley " in order to 

 get satisfactory yields of alfalfa a large amount of water must be supplied 

 during the season, [and] it must be supplied frequently enough to prevent a 

 drying of the surface soil on the one hand and water-logging of the soil on the 

 other. This desirable condition can only be accomplished by conforming the 

 grade of the land, the frequency of irrigation, the size of the field, and the 

 head of water used to the types of soil to be handled. . . . 



" The great danger in all sandy or porous soils is that too much water will 

 be applied and a high water table thus formed. This condition is already prev- 

 alent in some sections where sand overlays clay. . . . The lands or borders 

 for irrigation on this type of soil should usually not exceed one-eighth of a 

 mile in length and, if necessary, not more than 25 to 30 ft. in width in order 

 that the water applied may reach the lower end without oversaturating the 

 upper end. . . . The exact length and width of the lands must depend on 

 the condition of the surface and the degree of porosity of the soil. 



" If the soil is very sandy, the lands should be both narrow and short in order 

 to allow a quick irrigation. In addition to using smaller lands than are now 

 being used, it would be an advantage in nearly all cases to use much larger 

 heads of water than are at present used on this type of soil. In other parts 

 of California a head of from 8 to 12 ft. is often run on to one land in order 

 to get quicls irrigation. ... A head of from 3 to 8 cu. ft. per second for the 

 very sandy soil and from 2 to 4 cu. ft. per second for the more compact sandy 

 loams would not be too great. 



"A soil auger can be very effectively used in determining the soil moisture 

 condition where one is uncertain regarding the moisture penetration. In cases 

 where the grade is less than 5 ft. to the mile in the directions in which the 

 lands are built, and it can be increased to from 8 to 10 ft. to the mile by 

 changing the direction of the lands, it should be done. . . . 



" The sandy loam soils are easily irrigated, although too much or too little 

 water is sometimes applied with the usual results. There is no good excuse, 

 however, for not having a good moisture condition in these medium soft soils. 

 If the alfalfa does not grow so rapidly as desired an investigation should be 

 made of the moisture condition in the soil by the use of a soil auger or a spade. 

 If the top soil appears too dry before irrigation it would perhaps be wise to give 

 the field an additional light irrigation between cuttings. If the lower strata 

 are saturated the recommendatons given for hard or clay soils should be fol- 

 lowed. 



" The problem on the hard type of soils is to get the water deep into the 

 soil in sufiicient quantities to maintain rapid growth. . . . Land should be 

 from an eighth to a quarter mile long, very seldom running one-half mile as is 

 now a common practice. It is difficult to handle water properly on long lands, 

 as a flooding of the lower end can seldom be avoided. On land that is com- 

 paratively flat borders 50 to 100 ft. apart are satisfactory, but when the land 

 is at all steep lands should be narrowed down to 25 to 30 ft. wide so that a 

 small head will cover the surface evenly. In order to get proper penetration it 

 is necessary to run a comparatively small head for a long time. Fields which 

 yielded from 2.5 to 3 tons per acre per year have been made to double the yield 

 through this system of irrigation. A small head of water requires a much 

 longer time to travel over the field than a larger head and allows of a better 

 penetration. Land which could be wetted only to a depth of 3 ft. when large 

 heads were used was successfully wetted to a depth of 5 and 6 ft. by the use of 

 smaller heads. The effect of smaller heads running for a longer time is more 

 noticeable with furrow irrigation than with flooding, but the effect is marked in 

 both cases. The grade of hard land should not be over 5 or 6 ft. to the mile. A 



