TRRIGATION EXPERIMENTS IN IDAHO. 83 
that this table may be used far more than the corresponding one 
(Table XVIII), which shows the average volumes of water applied to 
porous soils. As has been stated elsewhere in this report, the irri- 
gation requirements of any particular crop on any soil are influenced 
by many factors and will be found to vary on different farms and 
a during different years, but as this table includes the results of 171 
| selected tracts of this particular type of soil, covering a period of 
four years, thus effectually neutralizing the individual differences of 
zen _| ray \ vine | guy ea 
ee 
DEW ja Feel. 
= 
ml 
Ss 2aP2 32.85 16-789 
Percent DP SAAMLVEIHO | 
(es 
Om 
Fig. 9.—A mounts of water required each month of the irrigation season by an Idaho project devoted 
to equal areas of grain and hay on medium clay loam or sandy loam soil. 
the seasons, of irrigators, and of the tracts themselves, it is consid- 
ered that the results will be found to be very dependable 
Keeping in mind that the table shows averages only, and that 
individual crops, farms, projects, and seasons are bound to depart 
from the average, the table shows that a project devoted to equal 
areas of (1) grain, orchards, and general root crops, and (2) hay, 
including alfalfa, clover, senna and pasture, on average southern 
Idaho soil should eran sufficient water so that an average of 2 feet 
can be retained on each and every irrigated acre during ane season. 
Of this quantity, which is exclusive of the precipitation, 0.01 foot in 
depth, or 0.5 per cent, will be required during the first half of April; 
