I2O THE SOIL SOLUTION 



reaction takes place in accordance with the following equation, 



Na 2 CO 3 + CaSO 4 = CaCO 3 + Na 2 SO 4 . 



Furthermore, it has been shown that calcium salts and especially 

 calcium sulphate exercise a marked ameliorating effect on the 

 action of other salts upon growing vegetation. 1 On the other 

 hand, the reaction indicated by the equation just given does not 

 run to an end with complete precipitation of the carbonate, and 

 the total amount of alkali is increased in the soil by the addi- 

 tion of the gypsum. Unfortunately, Hilgard's suggestion has 

 not yet acquired the sanction of satisfactory field demonstration, 

 although it would seem to merit more consideration than has 

 been given it. Inasmuch as lime is generally a prominent con- 

 stituent of soils containing black alkali, it is possible that the 

 maintenance of good drainage and aeration in the soil is itself 

 the best corrective of black alkali. 



The best use of alkali soils involves irrigation, and it is in 

 the application of irrigation waters that management of alkali 

 soils finds its most highly developed and most important ex- 

 pression. With light sandy soils it has sometimes been found 

 practicable to add sufficient water to carry the alkali down into 

 the soil to such a depth that the crop is well advanced toward 

 maturity before the alkali again rises in sufficient amounts to 

 prove seriously detrimental to the more advanced crops which are 

 generally far more "alkali resistant" than the young seedlings 

 or the germinating seeds. In some cases this procedure can be 

 practiced for a number of years without greatly increasing the 

 seriousness of the alkali conditions, and it may be justified, for 

 a time at least, by economic considerations. Ultimately, how- 

 ever, and more quickly with heavy than with light soils, increas- 

 ing amounts of alkali must be brought into the surface soil, and 

 this method of irrigating should not be considered as anything 

 more than a temporary expedient. The only procedure which 

 1 With the salts occurring in alkali, it is a generality that the effects 

 produced on higher green plants are relatively less wjtih mixtures than 

 with an equivalent amount of a single salt. It has recently been shown, 

 however, that the contrary is true for at least some kinds of bacterial 

 flora. See, On the lack of antagonism between certain salts, by C. B. 

 Lipman, Bot. Gaz., 49, 41-50 (1910). 



