88 TRANSACTIONS OF THE 
range. Differences in drainage of the soil, the kind of 
alkali, the quantity of water used, and several other 
factors make definite limits impossible. The water in 
streams may hold only a small quantity of salts in the 
spring when it comes direct from the melting snows, but 
later in the summer when it is most needed for irrigation 
the alkali content may have reached a dangerously high 
point because of seepage and return waters. This 
fluctuating salt content of the streams may further com- 
plicate the problem for streams which vary considera- 
bly in volume; they may fall within the limits of safe 
water during part of the year and be dangerous at other 
times. 
A soil with good drainage is seldom troubled with 
alkali. Such a soil, without being materially injured, 
could be irrigated with alkali water too strong to be suc- 
cessfully used on more impervious ones. If we can find a 
means to make use of the stronger alkali irrigation waters 
on the sandy or well drained soils and reserve the purer 
waters for the more impervious but richer loam and clay 
soils, great good will be accomplished. 
An arbitrary limit for the quantity of salts which may 
be present in an irrigation water without causing a rapid 
deterioration of the land due to alkali, may greatly assist 
in classifying waters as safe or unsafe for general irriga- 
tion purposes provided the modifying factors are taken 
into consideration. In California where there is more 
trouble from sodium carbonate, or black alkali, than is 
found in Utah, the limit for safe irrigation water is 
placed between 600 and 700 parts of alkali salts to each 
million parts of water or between 0.06 and 0.07 per cent. 
Where the main salt is sodium carbonate, as small a 
proportion as 300 to 500 parts might prove injurious. 
Utah waters, however, are troubled mainly with the 
less harmful sodium chloride and sodium sulphate. Under 
Arizona conditions where the salts are mostly sodium 
sulphate and sodium chloride in much the same pro- 
portion as in Utah waters and where the drainage is 
fairly good, as much as 1,000 parts per million is not con- 
sidered entirely unsafe to be used for irrigation. 
In New Mexico the water of the Pecos River which 
contains proportionately more sodium sulphate than the 
