THE CHEMICAL COMPOSITION OF SOILS 



NITROGEN AND ASH ELEMENTS 9 



The facts that plants feed on humate compounds, and 

 decaying animal and vegetable matter produce humates 

 from the inert potash and phosphoric acid of the soil, 

 have an important bearing upon crop production in 

 pointing out a way by which inert plant food may be con- 

 verted into more active and available forms. This 

 also explains that stable manure is valuable partly 

 because it makes the inert plant food of the soil more 

 available. 



117. Mineral Matter combined with Humus. - - When 

 the humus compounds are separated from a soil, they 

 contain appreciable amounts of phosphorus, potassium, 

 and compounds of other elements which are soluble in 

 the reagents used for obtaining the humus. If the 



