THE SOIL AS AN ASSET 



The density of the solution thus obtained 

 practically remained constant after the first 

 leaching, and was almost identical in its con- 

 tent of phosphoric acid and potash with a solu- 

 tion obtained by leaching the soil itself. An- 

 other method even more exact is by measuring 

 the electrical resistance of distilled water as it 

 leaches through rock particles or a sample of 

 soil. Continued experiments by this method, 

 too, show that the percentage of "plant food" 

 entering solution remains practically constant. 



The theory that all soils contain "plant 

 food" in inexhaustible quantities, and that 

 these minerals are at all times available by 

 solution or hydrolysis, was not suggested 

 originally by the scientists of the Bureau of 

 Soils. It was first put forth as a possibility 

 by Samuel W. Johnson. ("How Crops Feed," 

 1884.) In a work treating with the general 

 phases of soil fertility he details a number of 

 experiments showing that successive and sep- 

 arate leachings of a soil sample gave practi- 

 cally uniform results. 



Professor Milton Whitney shows (Soils of 

 the United States, Bulletin 55, Bureau of 

 Soils) that, in the average soil solution ob- 

 tained by contact with water and the soil 



