ALKALI SOILS 



337 



Table LXXVII 



effect of ceetain concentrations of salts on ceops. ex- 

 pressed in parts per million. 



Condition 



NaCl 



ISTa^COa 





Wheat 



Babley 



Rye 



Wheat 



Barley 



Rye 



Grermination affected. 

 Grermination prevented 



G-rowth affected 



Growth prevented . . 



500 

 2000 



500 

 2000 



1000 

 2500 



1000 

 2000 



1000 

 4000 



1500 

 2000 



3000 

 5000 



1000 

 4000 



2500 

 6000 



1500 

 4000 



2500 

 5000 



2500 

 4000 



containing considerably more than two-tenths per cent of al- 

 kali. Timothy, smooth brome, and alfalfa are the cultivated 

 forage plants most tolerant of alkali, although they do not 

 equal the native grasses in this respect. Cotton also tolerates 

 a considerable amount of alkali. 



Loughridge,^ after experiments and observation for a num- 

 ber of years, has obtained data regarding the resistance of 

 various crops to the several alkali salts. His results are given 

 in part as follows, expressed in pounds to an acre to a depth of 

 four feet. (See table LXXVIII, page 338.) 



Although in general the results as to the resistance to alkali 

 of the various crops are so conflicting, the Bureau of Soils,^ 

 in its alkali mapping, has been able to make a rough classifi- 

 cation as follows. (See table LXXIX, page 338.) 



178. Conditions that influence the effect of alkali. — It 

 has already been mentioned that organic matter and a high 

 moisture content of the soil tended to alleviate alkali toxicity. 

 Should, however, a previously wet soil become dry, the solu- 

 tion, originally very dilute, would become concentrated and 



^Loughridge, B. H., Tolerance of ATkali ly Var%ous Cultures; Calif. 

 Agr. Exp. Sta., Bui 133, 1901. See also Kearney, T. H., and Harter, 

 L. L., Comparative Tolerance of Various Plants for the Salts Com- 

 mon in AlJcah Bo%ls; XI. S. Dept Agr., Bur. Plant Ind., Bui. 113, 1907. 



* Dorsey, 0. W,, AlJcaU Soils of the United States; XT. S. Dept. Agr., 

 Bur. Soils, Bui. 35, pp. 23-25, 1906. 



