THE PLANT-FOOD THEORY OF FERTILIZERS I/ 



off are not uncommon. But that such a condition is general 

 or that it can be associated generally with a decreased content 

 in the soil of any particular mineral substance or substances, is 

 a conclusion not sustained by the available data. 



The plant-food theory of fertilizers must now be regarded as 

 entirely insufficient. Granting that it has been useful in the 

 past and has occasioned much valuable work, it seems to have 

 reached the point which another simple and temporarily useful 

 theory, the phlogiston theory of combustion, reached shortly 

 before the plant-food theory of fertilizers was evolved. Just as 

 the phlogiston theory passed away when the elementary nature 

 of oxygen was established and Lavoisier taught the scientific 

 world to use the balance, so the plant-food theory of fertilizers 

 must pass with increasing knowledge of the relation of soil to 

 plant and the application of modern methods of research to the 

 problem. 



