IRRIGATION EXPERIMENTS IN IDAHO. 23 
creased, as there is no appreciable break in the curve within the limit 
of the experiments. This curve shows again that alfalfa and clover 
require much larger supplies of water than grain, but the increase in 
the yield of alfalfa is not proportional to the increase in the water 
applied. Notwithstanding the fact shown by the curve, that the 
yield continues to increase with increased quantities of water, other 
considerations, such as the danger of water-logging land and the 
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Fie. 4.—Curve based on yields and amount of water applied to 77 individual fields of alfalfa on clay 
loam soils in Idaho, during 5 seasons, 1910 to 1914. 
limitation of the acreage which can be irrigated with a given water 
supply, would make it appear somewhat Alois tail whether more than 
3 a per acre should ever be allotted to alfalfa on medium clay loam 
so 
The alfalfa curve (fig. 4) was made up from observed data by first 
plotting all points on the sheet, after which points representing dif- 
ferent plots of each experiment were connected up by straight lines 
similar to the method used with the grain curve (fig. 3). The depths 
-13653°—Bull. 339—16——4 
