IRRIGATION EXPERIMENTS IN IDAHO. 



41 



lie reason that the water is absorbed so rapidly that it can not be 

 Dreed over the field. Where water can be conducted in pipes or 

 umos to within 100 or 200 feet of the farthest part of the field to 

 rhich it is to be applied, a method common among southern Cali- 

 )rnia orange growers, largo heads are not necessary, but where sur- 

 ice irrigation is practised on large field units of porous or semiporous 

 ail, the use of large heads is imperative if economy of water is to be 

 scured. The lack of efficiency of small irrigation heads was shown 

 y several of the experiments which were included in the investiga- 



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0=Soil more moist than normal prior to these irrigations. 



Fig. 11.— Effect of size of irrigation head upon amount required per application, based upon results of 

 an experiment upon 4.3 acres of porous gravelly loam soil in Boise Valley planted to pasture. 



ion. The average size of the irrigation head which is used for nearly 

 11 purposes in the larger portion of Idaho seldom exceeds 1 to 2 

 econd-feet, yet the use of heads three or four times this size would 

 ive a much higher efficiency, particularly if the soil is inclined to be 

 t all porous. With rather impervious soils there is not such a loss 

 1 efficiency. The smaller the size of the head and the greater the 

 istance water is run the larger the irrigation requirement. The 

 ccompanying curve (fig. 11) based on an experiment conducted by 

 V". G. Steward, of the Boise project, United States Reclamation Serv- 

 3e, clearly indicates the saving that may be made by using large 

 Leads for the irrigation of porous soils. 



