394 Journal of Agricultural Research vol. xx, no. 5 



SUMMARY 



(i) Seasonal studies on cropped and uncropped soils have shown that 

 water extracts reflect the principal fluctuations taking place in the soil 

 solution as indicated by the freezing-point method. 



(2) A soil extract is composed chiefly of the solutes present in the 

 soil solution plus substances dissolved from "adsorbed" or easily soluble 

 components of the soil. This latter fraction of the soil extract is depend- 

 ent in part on the concentration and composition of the soil solution, 

 since the solutes of the latter exert a depressing effect on the solubility 

 of certain soil constituents. This fact is believed to be of great impor- 

 tance in studies of chemical equilibria in soils. 



(3) A new method is suggested for indicating the relations between 

 the chemical elements in the soil solution. Extracts were prepared 

 which did not change appreciably in composition or concentration on 

 contact with the soil. The consideration of the equilibria involved sug- 

 gests the probability that the ratios between most of the important 

 elements are very similar in concentrated soil extracts and in the soil 

 solution. It is concluded that analyses of suitable soil extracts and 

 determinations of freezing-point depressions may frequently permit a 

 calculation of the concentration and approximate composition of the 

 soil solution. 



(4) Various methods of making water extracts have been compared. 

 The data obtained suggest that in seasonal studies extracts should 

 be made with the smallest proportion of water to soil practicable and 

 with the time of contact limited to that necessary for thorough admix- 

 ture. In routine work 1 to 1 or 1 to 5 extracts are convenient and 

 satisfactory. 



(5) Further experimentation has confirmed previous conclusions that 

 the soil solution fluctuates in composition and concentration with every 

 environmental change and with crop growth. 



LITERATURE CITED 

 (1) Bouyoucos, George J. 



1917. CLASSIFICATION AND MEASUREMENT OF THE DIFFERENT FORMS OP WATER 

 IN THE SOIL BY MEANS OF THE DILATOMETER METHOD. Mich. Agr. Exp. 



Sta. Tech. Bui. 36, 48 p., 5 fig. 

 (2) 



1919. RATE AND EXTENT OF SOLUBILITY OF SOILS UNDER DIFFERENT TREAT- 

 MENTS and conditions. Mich. Agr. Exp. Sta. Tech. Bui. 44, 49 p. 



(3) and Laudeman, W. A. 



1917. the freezing-point method as a new means of studying velocity 

 OF reaction between soils and chemical agents and behavior 

 of equilibrium. Mich. Agr. Exp. Sta. Tech. Bui. 37, 32 p. 



(4) and McCool, M. M. 



1916. the freezing-point method as a new means of measuring the con- 

 centrations OF THE SOIL SOLUTION DIRECTLY IN THE SOIL. Mich. Agr. 

 Exp. Sta. Tech. Bui. 24, p. 592-631,-2 fig. 



