THE SOIL AS AN ASSET 215 



quantities. They do assert, however, that the 

 function of commercial fertilizers is some- 

 thing infinitely more complex than the theory 

 of Liebig as taught to-day would lead one to 

 suppose; and that of all the profound in- 

 fluences the accepted chemical fertilizers exert 

 on the soil, that of supplying "plant food," 

 as such, is probably among the least impor- 

 tant. 



The old theory of infertility being due to 

 insufficient minerals in available form has been 

 so thoroughly accepted as a sufficient explana- 

 tion that the nature of the organic constituents 

 of the soil, and their influence in affecting fer- 

 tility, were spheres of research that were neg- 

 lected for a long time. The federal Bureau 

 of Soils is the first body of scientists in the 

 world to devote systematic study to this side 

 of the question, and as the result of their re- 

 searches they have established the fact that the 

 organic element is quite as important as the 

 mineral element in explaining fertility. The 

 part played by molds, bacteria, enzymes, "the 

 unseen flora and fauna of the soil," and won- 

 derfully complex organic compounds, either 

 tonic or toxic, in their effects on plants, has 

 been the subject of this investigation, and a 



