246 



SOILS. 



breakage, and leakage due to varying pressure in the supply pipes or 

 reservoirs ; as well as from even slight earthquake tremors, undermining 

 by water or by the burrowing of animals, and many other accidents 

 which do not affect an iron pipe system. The pipes must in any case, 

 of course, be laid deep enough to be out of reach of the deepest tillage ; 

 therefore not less than one foot, and preferably eighteen inches. A 

 proper construction of the outlets, permitting of exact regulation of the 

 flow and ready operation from above ground, as well as preventing 

 their being clogged by earth, rust, roots or burrowing animals, insects 

 .etc., is of course of the greatest importance. A variety of devices for 

 this purpose is already on the market. 



QUALITY OF THE IRRIGATION WATER. 



Soli nc 11 \ifcrs. Considering the large amount of water 

 annually used in irrigation, among the most needful precau- 

 tions to be observed by the irrigator is in the testing of the 

 quality of his water-supply. First among the points to he 

 noted is the possible content of soluble " alkali " salts. \Yhile 

 in most cases what is called the " rise of the alkali " is clue to 

 the salts already contained in the soil and subsoil, in but too 

 many the evil is either brought about, or greatly aggravated, 

 by the excessive saline contents of the water used in irrigation. 

 The effect- of the use of saline irrigation water (containing 

 in this case about 100 grains per gallon, or 1700 parts per 

 million) are shoun in the accompanying plate. The predom- 

 inant ingredients of these alkali salts were common salt and 

 carbonate of so, la. In the lands near < < vona. Cal.. where this 

 case was observed, the original alkali-content of the soil was 

 about .2500 pounds per acre in four feet depth, and had been 

 just quadrupled, with the result*- -hown : viz., complete de- 

 foliation of the orange trees, while on the <ame land, where 

 the trees had been irrigated with good artesian water, the 

 orchard was in fine condition. 



Limits of Salinity. It ^ not < a ign a definite limit 



of mineral content beyond which water should be considered 

 unfit for irrigation purposes; partly because of the differences 

 in the kind of the mineral salts, partly because the nature of 

 .the soil and the amount of water at command, materially in- 

 fluence its availability. 



