400 SOILS: PROPEBTIBS AND MANAGEMENT 



in a semiarid region, the natural rainfall will in time 

 effect the removal. 



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

 depth that soluble salt in the soil beneath them will not 

 readily rise to the surface. This will depend on those 

 properties of the soil governing the capillary move- 

 ment of water. Three or four feet in depth is usually 

 sufficient, but the capillary movement 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 satisfactory condition. 



Crops that will stand flooding may be grown during 

 this treatment, and they will serve to keep the soil 

 from puddling, as it is likely to do if allowed to become 

 dry on the surface. If crops are not grown, the soil 

 should be harrowed between floodings. The operation 

 should not be carried to a point where the soluble 

 salts are reduced below the needs of the crop, or so 

 low that they lose entirely their effect on the retention 

 of moisture. 



313. Correction with gypsum. — The use of gypsum 

 on black alkali land has sometimes been practiced for 

 the purpose of converting the alkali carbonates into 

 sulfates, thus ameliorating the injurious properties of 

 the alkali without decreasing the amount. The quantity 

 of gypsum required may be calculated from the amount 

 and composition of the alkali. The soil must be kept 

 moist, in order to bring about the reaction, and the 



