278 
Journal of Agricultural Research 
Vol. XXI, No. 4 
(8) When irrigation water contains more sodium and potassium than 
calcium and magnesium there is danger that its continued use may cause 
the land to become hard and impermeable to water. 
(9) Some of the important supplies of irrigation water in the United 
States carry more sodium and potassium than calcium and magnesium, 
and difficulties of hardness and impermeability of the soils are developing 
from the use of such water. 
(10) It is believed that these difficulties may be remedied through the 
use of calcium or aluminum in soluble form applied either to the land or 
in the irrigation water. 3 
