532 SOILS. 



notably of common salt and Glaubers salt, led some to the con- 

 clusion that the acidic ingredients are the chief determin- 

 ing factors. Moreover, it was soon found that a single salt 

 is more injurious than a mixture of several, such as sea 

 water. This also led to the inference that the varying degree 

 of dissociation of these salts essentially influences the effects. 



Kearney and Cameron have investigated these relations, 1 and hav< 

 by artificial cultures in solutions of varying concentration and com- 

 position studied the behavior of plant roots and the limits of theii 

 endurance. They found for the several salts occurring in alkali soils, 

 taken separately, the following figures, in 100,000 parts of water: 



Magnesium sulfate 7 



" chlorid 12 



Sodium carbonate 26 



" sulfate 53 



" chlorid 116 



" bicarbonate 167 



Calcium chlorid ij377 



It will be noted that in many respects the results given in this table 

 stand in marked contrast to the facts observed in alkali lands every- 

 where ; and therefore while interesting physiologically, are not directly 

 applicable to practice. Magnesium sulfate, which according to this 

 table is the most injurious of all, is a common ingredient of alkali lands 

 from Wyoming to New Mexico, as also is sodium sulfate ; yet there, 

 as well as in the Musselshell valley in Montana, and at many other 

 points, it shows no specially deleterious action either upon native or 

 cultivated plants, and in Europe as well as in New England the mineral 

 kieserite is freely used as a fertilizer at many points. That sodium 

 sulfate should be twice as harmful as sodium chlorid or common salt, 

 and half as harmful as the carbonate or black alkali, is again wholly 

 contrary to actual experience, which as shown elsewhere in this chapter, 

 indicates that the majority of plants will tolerate between three and 

 four times as much of sodium sulfate as of common salt ; while the ratio 

 of tolerance as against the carbonate seems sometimes to rise as high 

 as ten to one. 



It is clearly evident, however, that it is the metallic or basic ingre- 

 dient that in the main determines the toxicity of these salts. The 

 universal presence of lime in some form in all alkali lands doubtless 

 1 Report No. 71, TJ. S. Deo't of Agriculture, 1902. 



