216 
tons) it follows that every grain of salt per gallon adds 22630 = 
314lbs. of salt to the ground whenever that amount of water is 
used in irrigation. 
It would be unsafe to use extensively and continuously for 
the purpose of irrigation a well or pond water containing more 
than 70 grains of salt to the gallon. Such an amount would mean 
an addition of about 2ewt. (22714lbs.) of salt to the aere, for each 
one-inch watering. Such a water used in the more arid regions, 
where rainfall is light, would soon accumulate in the surface of 
the ground an amount of salt which would prove injurious to 
vegetation, and 10 irrigations of one inch each would add to the 
soil over a ton of salt, which, added to the amount of that sub- 
stance already in the ground, would make it sterile unless the soil 
is light and the drainage efficient. 
In the coastal districts, where the rainfall is more abundant, 
a water containing 50 grains of salt to the gallon could be used 
pretty freely for irrigation, provided the soil is of a light and 
porous nature and is well drained. But if used on stiffer soil it 
would, in the course of a few years, bring the amount of salt up 
to danger point. 
A water containing 10 to 12 grains of common salt to the 
gallon is often used for all domestic purposes. 
In a previous chapter dealing with the limits of salt in water 
the maximum amount of chloride of sodium in potable and stock 
water and water for irrigation, as suggested by Mr. E. «A. Mann, 
the State Analyst, is given more fully. 
' 4 
Factors WHIcH INFLUENCE IRRIGATION, 
No cast-iron rule can be laid down regarding the amount of 
water necessary for obtaining the best results from a given crop. 
The rainfall, the depth and nature of the soil and of the sub- 
soil, the particular variety and age of the trees, the climate, the 
quantity as well as the quality of the water at command, and the 
means and facilities of bringing water on to the land all require 
consideration. 
Speaking generally, a rainfall of 20 inches on deep loam fairiy 
rich in vegetable matter, and possessing good absorbing and reten- 
tive power, may prove sufficient for an orchard planted with 
deciduous trees, provided that amount of moisture is well tended, 
and by good cultivation prevented from escaping by evaporation. 
Under similar circumstances, 25 inches may do for evergrecus, 
such as citrus trees, which require more water, 
On deep, dry, sandy, or limestone formation, however, or on 
thin soil overlying solid rock, the plants would very likely show 
signs of distress even with a greater amount of rainfall, 
