Dec. 27, 191 5 Petrography of So7ne North Carolina Soils 581 



combe field the content of phosphoric acid is somewhat less than that of 

 the Cecil clay loam at the Iredell farm, yet in the latter soil phosphorus is 

 the limiting element; but this is not the case in the former, owing doubt- 

 less to the way this constituent is held in the two soils. The supply of 

 phosphorus must be stored in the organic form. There is practically no 

 apatite in this Norfolk soil, while it is readily encountered in the residual 

 soils of the Piedmont Plateau, occurring both free and included in quartz 

 and other minerals. 



CONCLUSIONS 



The results of this and other work on the subject indicate that the 

 following conclusions can be drawn, some of which are undoubtedly 

 applicable to other than North Carolina conditions. 



Wide variations in mineralogical composition are found between the 

 soils of the Appalachian Mountains, Piedmont Plateau, and Atlantic 

 Coastal Plain. There is unquestionably a greater supply of minerals 

 which carry the inorganic plant-food constituents in the Mountain soils 

 than are found in either the Piedmont Plateau or the Coastal Plain. 

 Though many of the former soils are derived from the same rocks as 

 those of the Piedmont province, the forces of erosion among those of the 

 mountains cause them to contain minerals more nearly the same as the 

 parent rocks than are found elsewhere. 



Definite information is required on the behavior of the various soil- 

 forming minerals to the forces of weathering before positive conclusions 

 can be drawn on the availability of the plant food carried by the different 

 minerals. 



The field results with the cotton plant indicate that there are some 

 relationships existing between the mineral component of the soil and the 

 requirements of this plant for the three inorganic fertilizer constituents, 

 phosphoric acid, potash, and lime. 



