ALKALI SOILS 341 



nate by various means some of the alkali. In the latter, meth- 

 ods of soil management are employed which will keep the salts 

 well distributed throughout the soil. In many cases soils 

 would grow excellent crops if the alkali could only be kept 

 well distributed through the soil layers so that no concentra- 

 tion that is toxic could occur, at least within the root zone. 

 In general, steps should be taken toward the control of alkali, 

 whether eradication is attempted or not. Under irrigation, 

 careful attention is always wise. 



181. Eradication of alkali. — Of methods designed at 

 least partially to free the soil of alkali the commonest are: 

 (1) leaching with under-drainage, (2) correction with gyp- 

 sum, (3) scraping, and (4) flushing. Of the various methods 

 for removing an excess of soluble salts, the use of tile drains 

 is the most thorough and satisfactory. When this method is 

 used in an irrigated region heavy and repeated applications 

 of water must be made, to leach out the alkali from the soil 

 and drain it off through the tile. When used for the ameliora- 

 tion of alkali spots in a semi-arid region, the natural rainfall 

 will often in time effect the removal. 



In laying tiles it is necessary to have them at such a depth 

 that the soluble salts in the soil beneath them will not readily 

 rise to the surface. This will depend on those properties of the 

 soil governing the capillary movement of water. Three or 

 four feet in depth is usually sufficient, but the capillary move- 

 ment should first be estimated. 



After the drains have been placed the land is flooded with 

 water to a depth of several inches. The water is allowed to 

 soak into the soil and to pass off through the drains, leaching 

 out part of the alkali in the process. Before the soil has 

 time to become very dry the flooding is repeated, and the 

 operation is kept up until the land is brought into a satis- 

 factory condition. 



Crops that will stand flooding may be grown during this 

 treatment, and they will serve to keep the soil from puddling, 



