4-02 Journal of Agricultural Research vol. xx, no. 5 



The effect of various salts on the flocculation of soils has been studied 

 in many investigations. Sharp * in an extensive series of observations 

 has presented evidence to show that a remarkable change is produced in 

 the physical state of the soil by the addition of various salts and sub- 

 sequent washing of the soil with water. This change in the degree of 

 dispersion of the colloids is attributed to the formation of new silicate 

 compounds which give to the soil its new properties. 



These investigations by Sharp have all dealt with rather extreme salt 

 effects, such, for example, as might occur in "alkali" soils or heavily 

 fertilized soils. So far as known, no study has been made of the changes 

 which may take place in soils because of the normal fluctuations in the 

 soil solution under varying conditions of cropping and season. In such 

 cases the total quantity of salts dissolved in the soil solution is extremely 

 small, and it might be questioned whether these could have any appre- 

 ciable effect on the physical state of the soil. However, an analysis of 

 the data presented by Stewart 2 and Hoagland 3 brings out the fact that 

 relatively enormous fluctuations may take place in the soil solution. 

 The growth of a crop, for example, in certain instances may reduce the 

 concentration of the soil solution to an extremely low point. Recently 

 McCool and Millar 4 have presented extensive data to show that in the 

 field very profound changes may occur in the soil solution as a result of 

 cropping, moisture variations, biological activities, rainfall, etc. Appar- 

 ently all of these fluctuations in the soil solution may be reflected in the 

 physical state of some at least of the soil constituents. 



Since the effect of cropping is to reduce the water-soluble constituents 

 of the soil and the concentration of the soil solution, it might be pre- 

 dicted on the basis of the foregoing discussion that soils which had been 

 cropped would show a physical condition distinctly different from the 

 same soils kept uncropped. In order to decide this point more definite 

 turbtditv determinations were made on a number of different soils. 

 Except that one tank of each soil had been cropped for four years and one 

 tank had been kept without crop for three years, the soils were maintained 

 under identical conditions. Originally both portions of the soil were from 

 one sifted, homogeneous mass. The details of treatment have already 

 been described in an article by Stewart. 5 Chemical analyses and conduc- 

 tivity measurements on water extracts, as well as freezing-point depres- 

 sions on the moist soil, all pointed to the fact that the uncropped soil 

 yielded a soil solution of higher concentration than did the cropped soil. 

 The data contained in Table I give evidence that these differences were 

 reflected in the physical state of the soils. It is particularly easy to 

 demonstrate this relation for the silty soils, but even the sandy soils 

 display the same tendency. 



1 Sharp, L. T. op cit. 4 McCool, M. M., and Millar, C. E. op. err. 



5 Stewart, Guy R. op. cit. 6 Stewart. Guy R. op. err. 



3 Hoagland, D. R. op. err. 



