IRRIGATION EXPERIMENTS IN IDAHO. 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 24 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 X VI.—Areas devoted to different crops. 
| : 
2 Eis Grain, potatoes 
Hay and pasture. | eiorehandiae 
District. Year. | ur Total. 
| Per cent | Per cent 
Tee. _ of total. | Area. | of total. 
; Acres. | Acres. Acres. 
Twin Falls South Side project........-.---- 1912 70,043 | 47.55 | 77,266 52.45 147,309 
«DO. [245 ae eon 1913 67, 115 44.95 | 82,196 55.05 | 149,311 
Seven Baise Valley projects. ..-.---.-...---- 1911 | 126,253 159.75 | 17,684 |~ = 40.25 43, 937 
pixeboise Valley projects.............---.--- 1912 | 24,492) 57.90) 17,804 42.10 42,296 
TORGT c cca 's eee ee TSTMS 0D el pe ee ae 194¥050) eae 382, 853 
A TORII 5 od Gate SEA Sec pene DRS a Niven eh AQVOS) eee SORODE |S Merc eee 
| | 
1 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.. 
