" Apr. 22, 1918 Biological A ctiviiies and Conceniraiion of Soil Solution 2 1 5 



measured the amount of the salt added but at the completion of the 

 period of growth extracted the soil with water and determined the 

 quantity of salt removable. They arrived at the following conclusion 

 (p. 869): 



The limit of tolerance of crop plants to the salt in the soil is determined by the quan- 

 tity of salt that can be recovered from the soil rather than by the quantity added 

 to the soil. 



The toxicity of sodium carbonate was much greater in beach sand than 

 in loam soil, and the loss of carbonate was much less in the sand than in 

 the loam. 



Bouyoucos and McCool ^ studied more in detail the action of salts in 

 soils and found that equal amounts of various salts added to different 

 soils result in widely different concentrations of the soil solution and 

 suggest that there is probably considerable change in the chemical 

 composition of the resulting soil solution. 



More definite information regarding the difference in end products 

 formed when salts come in contact with different soils is furnished by 

 McCool and Wheeting,^ who show that the amounts of water-soluble 

 calcium, iron, and magnesium in soils through which various salts have 

 diffused are quite different and that the quantities of these elements 

 in the layers of soil at various distances from the salt deposit are variable. 



This interaction of soil and salt has seemingly been overlooked by some 

 investigators in accounting for the toxic action of salts ; and it was with 

 the hope of obtaining more evidence as to whether osmotic pressure, the 

 toxic properties of the salt itself, or the products of the interaction of 

 the soil and salt was responsible for the effects noted that the following 

 experiments were conducted. 



EXPERIMENTAL WORK. 



Three soils were used in this work: A Coloma sand, a Miami sandy 

 loam, and a Clyde clay loam. The soils were brought to the laboratory, 

 dried, passed through a 20-mesh sieve, mixed thoroughly, and stored 

 in the dark. As needed, loo-gm. samples were weighed into sterile, 

 covered tumblers and thoroughly mixed with 2 gm. of finely grotmd 

 dried blood. The salts were applied in solution. The most concen- 

 trated solution was made by weighing out the correct amount of the 

 salt and dissolving it in distilled water. The solution of next lower 

 concentration was made by drawing off a portion of the first solution 

 and making it up to the required volume by weight. The third solution 

 was made from the second in a similar manner. The solutions were 



' Bouyoucos, G. J., and McCool, M. M. the FKEEzmG-poiNT method as a means op measuring 



THE CONCENTRATION OF THE SOU, SOLUTION DIRECTLY IN THE SOIL. Mich. Agr. Exp. Sta. Tech. Bui. 34, 



p. 592-631, 2 fig. I916. 



'McCooL, M. M., and Wheeting, L. C. movement of soluble salts through soas. In Jour. 

 Agr. Research, v. n, no. ii, p. 531-547, 5 fig. 1917. 



