288 THE FUTURE OF ARID LANDS 
prevent the accumulation of salts by irrigation, and to prevent 
the occurrence of high water-table conditions. 
With respect to water management, irrigation should be con- 
trolled in such a way that a favorable salt balance will be main- 
tained. This occurs when the output of salts for a given area 
exceeds the input (4). Enough water, in excess of the consumptive 
use or evapo-transpiration requirements, should be applied to 
remove from the irrigated area approximately as much salt as is 
transported onto the land by the irrigation water. Since plants 
absorb water from the soil solution but take in only a small 
proportion of the dissolved constituents, there will be a gradual 
increase in the salinity of the soil unless the amount of water 
applied to the land is sufficiently in excess of the plant require- 
ments and the losses of water by surface evaporation so that 
salts in solution are carried out of the root zone and into the under- 
drainage. 
Successful water management involves two operations which 
are opposed to one another. In the first instance, sufficient water 
must be applied to insure the movement of salts through the 
profile so as to prevent an accumulation of salts and maintain a 
favorable salt balance. On the other hand, excessive use of water 
must be avoided in order to prevent the development of high 
water-table conditions and the consequent drainage problems. 
A second consideration in water management is the possibility 
of using “blending”? methods in cases where some of the water 
supplies are too saline, but other supplies of good quality are 
available. If soil properties and drainage conditions are satisfac- 
tory, waters of high salinity may be used by “blending,” or 
mixing, waters of poor and good quality in such proportions that 
the salinity of the water applied to the land has been reduced to 
reasonably satisfactory limits. 
The selection of appropriate crops may serve to ameliorate a 
situation where the use of saline water has resulted in saline 
conditions. Field and plot tests at the Salinity Laboratory and 
elsewhere have demonstrated that there is a wide difference in 
the relative salt tolerance of the crops grown in the western states. 
For example, the chances for satisfactory yields of field crops 
