Dec. i, 1920 



Effect of Season and Crop Growth on Soil 



401 



physical state of the soil. That this correlation is only approximate is 

 not difficult to explain, even if we assume that the factors mentioned 

 above are the only ones to be considered. The quantity of suspended 

 material obviously can not bear an exact relation to the concentration 

 of the solution throughout all ranges. At a certain point the supernatant 

 liquid will become almost clear, and while further increases in the con 



Fig. , 



WEEKS 



-Effect of crop on physical state and electrolyte concentration of the water extract of the soil. 



centration of electrolytes will diminish the resistance almost proportion- 

 ally, no further change can be shown in the physical state of the soil as 

 measured by the present method. Moreover, the conductivity is a re- 

 sultant measurement expressive of the concentration or mobility of all 

 the ions present. It is not true, however, that equivalent quantities of 

 different ions have equal effects on the colloidal state of the soil. 



