UTILIZATION AND RECLAMATION OF ALKALI LANDS. 



459 



rid of, the loss of a few inches of surface soil being of little 

 moment in the deep soils of the arid region. Another method 

 affording partial relief is to flood the land for a sufficient 

 length of time to carry the alkali three or more feet below the 

 surface, then carefully preventing its reascent by suppressing 

 evaporation (see this chapter, p. 455) as much as possible. 

 The best of all, the final and universally efficient remedy, is to 

 leach the alkali salt out of the soil into the country drainage; 

 supplementing by irrigation water what is left undone by the 

 deficient rainfall. 



It is not practicable, as many suppose, to wash the salts off 

 the surface by a rush of water, as they instantly soak into the 

 ground at the first touch. Nor is there any certain relief from 

 allowing the water to stand on the land and then drawing it off; 

 in this case also the salts soak down ahead of the water, and 

 the water standing on the surface remains almost unchanged. 

 In very pervious soils and in the case of white alkali, the 

 washing-out can often be accomplished without special provis- 

 ion for underdrainage, by leaving the water on the land suffi- 

 ciently long. But the laying of regular underdrains greatly 

 accelerates the work, and renders success certain. 



Lcaching-Down. In advance of underdrainage, it is quite 

 generally feasible, where the land has been leveled and diked 

 for irrigation by surface flooding, to leach the salts out of the 

 first three or four feet by continued flooding, thus taking them 

 out of reach of the crop roots, or at all events giving the seed 

 an opportunity to escape injury from alkali. This plan is es- 

 pecially effective in the case of alfalfa, the young seedlings of 

 which are very sensitive, while the grown plant is rather re- 

 sistant. In order to obtain this relief so as to know what is 

 being accomplished, the farmer should ascertain beforehand 

 how fast water will soak down in his ground ; a for in heavy clay 

 soils, and especially in those containing black alkali, the soak- 

 age is sometimes so slow that the upward diffusion of the salts 

 keeps pace with the downward soakage ; in which case nothing 

 is accomplished by flooding, and underdrainage is the only 

 remedy. But in most soils of the arid region flooding from 

 three days to a week will remove the alkali beyond reach of 

 the roots of ordinary crops. If subsequently irrigation is done 



1 See p. 242, Chap. 13. 



