THE SOIL AS AN ASSET 229 



increased the "available" plant food of his 

 acres? The foregoing experiment on his own 

 soil would prove that the addition of salts of 

 potash and phosphorus has not effected any 

 additional concentration in the soil solution; 

 and it is an established fact that a plant can- 

 not extract food from the soil unless that food 

 is in solution. 



This experiment suggested a new world of 

 experiment to the investigators. The prob- 

 lem of why soluble salts cannot be extracted 

 from the soil by water is something aside from 

 the discussion at this point. The mere fact 

 that they cannot is of first importance, coupled 

 of course with the fact that the concentration 

 of the soil solution remains practically con- 

 stant, no matter how much soluble salt may be 

 in the soil. 



It is objected in this connection that the 

 test is not fair, because the first sample of soil 

 surely contained "soluble" or "available" 

 minerals innately, and it was these that entered 

 into solution to saturation. 



In answer to this objection, the experiment 

 can be conducted not with soil itself, but with 

 rock-forming minerals. They can be obtained 

 from any museum collection. The rock-form- 



