——_—  - 
IRRIGATION EXPERIMENTS IN IDAHO. Dil 
per acre from the land and a low return per acre-foot of water de- 
pends on the relative cost of land and water, the cost of production, 
and other factors. The solution of the problem in each instance 
depends on local economic conditions. 
The curves presented in figure 7 show the average results secured 
from 21 plots of alfalfa grown during five years at the Gooding ex- 
periment station, and also of three plots grown at Buhl, 30 miles 
away, on the same type of soil. These curves show that alfalfa re- 
quires large quantities of water and that the yield increases as the 
Fic. 6.—Effect of different amounts of water on the yield of straw, Gooding experiment station. 
supply of water is increased, sufficient water not having been ap- 
plied to determine at what point the excessive supply begins to de- 
crease the yield of alfalfa. The lower curve shows yields of hay per 
acre-foot of water applied and imdicates that while less efficiency is 
secured from water where large applications are made, the decrease 
is not nearly so pronounced as when they are applied to grain. These 
curves and the data from which they were constructed are typical of 
the results secured throughout other districts of Idaho on this same 
_ type of soil and show that if yield alone is considered it is difficult to 
apply too much water to alfalfa, provided no more is applied at one 
time than will be promptly absorbed by the soil. The proper 
_ quantity to allow for alfalfa, however, as with the grains, will be 
determined by local economic conditions. 
