2 BULLETIN 339, U. S. DEPARTMENT OF AGRICULTURE. 



PLAN OF INVESTIGATION. 



The investigation was planned to show the actual irrigation require- 

 ments of the various soils and crops common to southern Idaho. 

 The staple crops — alfalfa, clover, pasture, spring and winter grains, 

 potatoes, and orchards — have all been represented. The fields had 

 a varying topography, with slopes ranging from 20 feet in 100 to 4 

 feet per mile. 



In order to make the results practical and dependable and such 

 as good farmers might obtain under average conditions it was 

 decided: (1) That the investigation must be conducted in the main 

 by men employed especially for the purpose and without outside 

 interests; (2) that the areas experimented upon must be compara- 

 tively large; (3) tliat the investigation must extend over several 

 years, so as to eliminate or neutralize the individual characteristics of 

 the different seasons; and (4) that the mere measurement of the 

 water applied to single tracts would be insufficient, for this would 

 not show the yield that might have been produced by a greater or 

 lesser application of water. 



SCOPE OF INVESTIGATION. 



As mentioned above, the study extended through four seasons, 

 during which time water was measured upon 529 individual tracts, 

 having a total area of slightly over 3,600 acres. In order to determine 

 the normal quantity used by the farmers when such use was unre- 

 stricted and not influenced in any way by the proximity of experi- 

 ments, the water applied by them to 28 other tracts, having a total 

 area of 1,306.8 acres, was measured with automatic water registers. 



The water diverted and used by seven different canal systems in 

 1911 and nine systems in 1912 was measured, and the areas irrigated 

 under them were determined. 



In a comprehensive study of the transmission losses of canals the 

 seepage losses in 118 sections of different canals with an aggregate 

 length of 278.3 miles were determined. The canals measured varied 

 in discharge from 0.07 to over 3,190 cubic feet per second, and in 

 cross section from 0.117 to 984 square feet. 



The percentage of nonirrigated or waste land in a typical project 

 was also determined, 16,067.8 acres located in two bodies being sur- 

 veyed for the purpose. 



The territory covered extends from Rigby, with an altitude of 

 4,950 feet, in the upper Snake River Valley, to Weiser, with an alti- 

 tude of 2,114 feet, on the western boundary of Idaho, a distance of 

 368 miles. 



