RATE AND EXTENT OF SOLUBILITY OF SOILS UNDER DIFFER- 

 ENT TREATMENTS AND CONDITIONS 



Technical Bulletin No. 44. 



BY GEORGE J. BOUYOUCOS. 



INTRODUCTION. 



A study of the rate and extent of solubility of soils is obviously of 

 the greatest fundamental importance both from the i^ractical as well 

 as the theoretical standpoint. In this study are involved the important 

 questions (1) of the velocity and amount of soil material going into 

 solution; (2) to what extent the solubility of soils follows the recognized 

 laws of solution such as the mass law, solubility law, etc., {?)) if the 

 solubility of soils attains equilibrium and the soil solution becomes 

 saturated and remains constant; (4) the difference in rate and extent 

 of solubility of soils under different treatments and state of fertility, etc. 



From the answers to these questions it can then be ascertained (1) 

 the rate at which the soils are able to give up material to the solution 

 for the use of the plants; (2) the rate and amount of material that is 

 likely to be lost through leaching; (8) the velocity at which soils are able 

 to recuperate after a thorough leaching or exhaustion by the growth of 

 plants, etc. All this information is of course of the greatest importance 

 in the study of the fertility of soils. 



Although a tremendous amount of work has been done on the quantity 

 of soluble salts in soils, very little work has been performed on the rate 

 and extent of solubility of soils. Indeed, there appears to be on record 

 no extensive, thorough and purposeful investigation upon the problem 

 except a few incidental experiments or indirect observations. 



As a result of this insulticient investigation our present knowledge of 

 the subject is very limited, contiicting and confusing. 



AVith the hopes of contributing, if possible, a definite and true solution 

 of the problem an investigation of it was undertaken. In this investiga- 

 tion a new method was applied, namely, the freezing point method. 

 This method appeared and has proved to be very ideal for the purpose. 

 The problem received a thorough study and it is the object of this bulletin 

 to present the results obtained. 



The investigation was begun in June, 1917. In February, 1918, or 

 nine months later, there appeared in the Journal of Agricultural Re- 

 search an article by D. R. Hoagland entitled 'The Freezing Point Method 

 as an Index of Variation in the Soil Solution Due to Season and Crop 

 Growth." In this article Hoagland presents one or two experiments 

 which were already independently done by the writers. It will be of 

 interest to state that the results of these respective experiments lead all of 

 us to draw identicarconclusions. 



