TRRICATloX EXPERIMENTS IX IhAIIO. 



31 



The average annual requirement of 2.49 feet of water per acre 

 is less than the amount required to produce maximum yields, as 

 shown by figures 4 and 7, where an application of 2\ feet pro- 

 duced yields of 5.25 and 4.86 tons per acre, respectively, with an 

 increasing yield as the quantity applied was increased. The curves, 

 however, do not show at what point economy demands that the 

 quantity applied be fixed, and it_ is believed that the table does 

 show this for economic conditions similar to those in Idaho. 



The United States census of 1910 showed average yields of irri- 

 gated alfalfa as follows: Idaho, 3.27 tons per acre; Oregon, 3.29; 

 Washington, 3.98; and California, 3.49, all other States having a 

 less average yield. Considering these average yields along with the 

 facts shown by both the table and the curves, and also the danger of 

 water-logging the land and the curtailment of the State's irrigated 

 area, it is believed that 2.5 feet of water per acre represents the proper 

 allotment for alfalfa on clay loam soil under economic conditions 

 similar to those of Idaho. 



Each of Tables XIV and XV shows the monthly and seasonal 

 requirements of only one class of crops. Hence, before the data con- 

 tained in either or both of them may be used for the determination of 

 the proper allotment on an entire project, it becomes necessary to 

 know what crops will be grown upon the project, for alfalfa and pas- 

 ture require so much more water than grains that the ultimate acre- 

 age of each particular class of crops becomes a dominant factor. In 

 order to throw light upon this subject and furnish an accurate basis 

 for combining the two tables to show the requirements of an entire 

 project, a census of several typical Idaho irrigation projects was 

 secured, the results being shown in Table XVI. 



'Table XVI. — Areas devoted to different crops. 





District. 



Year. 



Hay and pasture. 



Grain, potatoes, 

 and orchard. 



Total. 



Area. 



Per cent 

 of total. 



Area. 



Per cent 

 of total. 



Twin Falls South Side project 



1912 

 1913 

 1911 

 1912 



Acres. 

 70,043 

 67, 115 



120,253 

 24, 492 



47.55 



44.95 



159.75 



57.90 



Acres. 

 77,266 

 82, 196 

 17, 684 

 17,804 



52.45 

 55.05 

 40.25 

 42.10 



Acres. 

 147, 309 



Do 



149,311 





43,937 

 42,296 









Total . r 





187, 902 



194.950 





382,853 









49.08 





50.92 











i This area and percentage was somewhat above normal on account of the comparatively large acreage 

 of bottom land that was seeded to pasture under some of those canals. 



Table XVI shows that under normal Idaho conditions almost 

 exactly one-half of the irrigated acreage is devoted to each class into 

 which the crops of the investigation have been divided. (See also p. 





