Sept. 10. 1917 Formation of "Black Alkali " 589 



(12) The alkali crusts that accumulate upon the soil in some irrigated 

 regions are due in part to the action of sodium salts upon calcium car- 

 bonate with the formation of sodium carbonate. 



(13) Barren, or "slick," spots are often due to the action of sodium 

 nitrate, sodium chlorid, or sodium sulphate upon calcium carbonate 

 with the formation of sodium carbonate. 



(14) Sodium chlorid and sodium sulphate have a protective action 

 upon organic matter in the presence of sodium carbonate. 



(15) A calcareous hardpan often produces black alkali. 



LITERATURE CITED 

 (i) Cameron, F. K. 



1901. son. soi^uTioNs: their nature and functions, and the classifica- 

 tion OP ALKALI LANDS. U. S. Dept. Agf. But. Soils Bui. 17, 39 p. 



(2) Briggs, L. J., and Seidell, Atherton. 



I90I. SOLUTION STUDIES OF SALTS OCCURRING IN ALKALI SOILS. U. S. Dcpt. 



Agr. Bur. Soils Bui. 18, 89 p., 10 fig. 



(3) DORSEY, C. W. 



1906. ALKALI SOILS OF THE UNITED STATES. A REVIEW OF LITERATURE AND SUM- 

 MARY OF PRESENT INFORMATION. U. S. Dept. Agt. Bur.Soil Bui. 35, 

 196 p., 13 fig. Bibliography, p. 58-60. 



(4) Harris, F. S. 



1916. SOIL alkali STUDIES. QUANTITIES OF ALKALI SALTS WHICH PROHIBIT 

 THE GROWTH OF CROPS IN CERTAIN UTAH SOILS. Utah. Agr. Exp. Sta. 

 Bul. 145, 21 p., 15 fig. 



(5) Headley, F. B., Curtis, E. W., and Scofield, C. S. 



I916. EFFECT ON PLANT GROWTH OP SODIUM SALTS IN THE SOIL. In JOUT. Agf. 



Research, v. 6, no. 22, p. 857-869, 8 fig. 



(6) HiLGARD, E. W. 



1914. SOILS. . . . 593 p., 89 fig. New York. 



(7) Lyon, T. L., and Fippin, E. O. 



1909. THE PRINCIPLES OP SOIL MANAGEMENT. 531 p., 157 fig. New York. 



4599°— 17 i 



