Dec. 27. 191S Petrography of Some North Carolina Soils sil 



interesting. These ham-shaped, isotropic particles are the remains of 

 some form of life that flourished here during the submergence of this 

 land. 



In the Orangeburg series occurs a higher content of minerals other 

 than quartz than is found in either the Norfolk or the Portsmouth series, 

 but still the amount is small. The soils of the Orangeburg series re- 

 semble the Norfolk in many respects, and the same general minerals are 

 encountered. 



The low content of other minerals than quartz in the soils of the 

 Atlantic Coastal Plain is in close agreement with the total chemical 

 analyses of the three plant-food constituents — phosphoric acid, potash, 

 and lime. Many chemical analyses of the soils of this province show the 

 above-named elements of plant growth to be exceedingly low. Not only 

 do there appear to be close relationships existing between the total chem- 

 ical analyses and their mineralogical complexity here, but in the soils 

 of the entire State. This would suggest that since the petrographic 

 methods have reached so high a state of development they may be used 

 with a fair degree of accuracy for estimating the amounts of the mineral 

 plant-food constituents carried by a soil. On account of the ease of 

 manipulation and the time saved in their use, they lend themselves 

 readily for such purpose; especially is this true in scanning soils for the 

 farmer. The information gained is usually not commensurate with the 

 time and expense involved in making "bulk analyses" of soils for 

 farmers. As a rule, it is not necessary that he know the exact number 

 of pounds of plant food contained in his soil; an approximation will 

 usually suflEice. A very close estimate as to the quantity of the elements 

 present may be easily secured with the microscopic methods; even 

 more, the way these elements are held is revealed. If more data were 

 at hand showing the availability of the various mineral elements of plant 

 growth furnished by the different soil-forming minerals, more definite 

 information could be obtained as to the fertilizer requirements of the 

 land with the microscope than by "bulk analyses." 



In a former publication ^ the writer submitted data from which there 

 appeared to be some relationships existing with certain crops between 

 the mineralogical and chemical composition of the soils of this State and 

 their requirements for the inorganic elements found in the usual ferti- 

 lizer mixture — namely, phosphoric acid, potash, and lime. Additional 

 evidence will be submitted along this line, using the cotton plant as the 

 indicator for measuring the relative densities of the soil solution. 



In Table II will be found the average results of seven years' fertilizer 

 treatments with cotton at the Iredell Substation, located upon typical 

 Cecil clay loam. 



1 Plummer, J. K. Relation of the mineralogical and chemical composition to the fertilizer requirements 

 of North Carolina soils. N. C. Agr. E.^. Sta. Tech. Bui. 9, 29 p. 1914. 



