THE WATER OF SOILS. 



249 



tience than American irrigators are ordinarily willing to be- 

 stow upon their work. Much depends of course not only 

 upon the character of the salts in the water, but also upon the 

 long experience had in the old irrigation regions. 



Mode of using Saline Irrigation U'aters. The fact that 

 abundant growths of native as well as cultivated plants may 

 sometimes be seen on the margins of " alkali lakes ' where 

 water of over a hundred grains of mineral salts per gallon 

 continuously bathes the roots, while the same plants perish at 

 some distance from the water's edge, points the way to the 

 utilization, in emergencies, of fairly strong saline waters; viz., 

 by the prevention of their concentration to the point of injury 

 by evaporation. It is clear that when such waters are used 

 sparingly, so as to penetrate but a few feet underground, 

 whence the moisture re-ascends for evaporation at the surface, 

 a few repetitions of its use will accumulate so much alkali near 

 the surface as to bring about serious injury. If, on the other 

 hand, the water is used so abundantly that the roots may be 

 considered as being, like the marginal vegetation of alkali 

 lakes, bathed only by water of moderate strength, no such in- 

 jury need occur; and what does accumulate in consequence of 

 the inevitable measure of evaporation occurring in the course 

 of a season, may be washed out of the land by copious winter 

 irrigation. 



This, of course, presupposes that the land, as is mostly the 

 case in the arid region, is readily drained downwards when a 

 sufficiency of water is used. When this is not the case, e. g., 

 in clay or adobe soils, or in those underlaid by hardpan, waters 

 which in sandy lands could have been used with impunity, may 

 become inapplicable to irrigation use. 



Apparent Paradox. The prescription to use saline waters 

 more abundantly than purer ones, in order to avoid injury 

 from alkali, though paradoxical at first sight, is therefore 

 plainly justified by common sense as well as by experience, in 

 pervious (sandy) soils; while in difficultly permeable ones, 

 their use may be either wholly impracticable, or subject to 

 j very close limitation. 



Sometimes the alternate use of pure and salt-charged water 



serves to eke out a too scant supply of the former. But in 



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