Dec. 37, 191S 



Petrography of Some North Carolina Soils 



579 



The 8-year average with cotton given in Table III again shows that 

 phosphoric acid is the controlHng element in these fertiUzer tests. When 

 potash and nitrogen are used in quantities, as in this experiment, only 

 sUght increases in yield are produced. The former constituent gave a 

 slightly greater average than did the latter. The average "bulk analy- 

 ses" of many samples of soil from these two fields, as well as from Norfolk 

 fine sandy loam, will be found in Table IV. 



Tabi,E IV. — Average quantity of the total plant-food coyistituents per acre in various types 



of soil 



SURFACE SOIIv TO DEPTH OP 6J/3 INCHES (2,000,000 POUNDS) 



Nitrogen 

 (N). 



Phosphorus 

 pentoxid 

 (P2O6). 



Potassium 

 oxid (K2O). 



Calciuta 

 oxid (CaO). 



Cecil clay loam 



Cecil sandy loam 



Norfolk fine sandy loam. 



Pounds. 

 I, 141 

 769 



Ptrunds. 

 1,155 

 503 



953 



Pounds . 

 7,213 

 2,994 

 3.087 



Pounds. 

 4,656 

 5,542 

 3,220 



SUBSOIL TO DEPTH OF 28 INCHES (8,000,000 POUNDS) 



Cecil clay loam 



Cecil sandy loam 



Norfolk fine sandy loam. 



19, 933 



26,512 



8,880 



A comparison of the yields of cotton on the two fields shows marked 

 similarity in fertilizer requirements though the fields are over loo 

 miles apart. These soils belong to the same series, though of decidedly 

 different texture, one being a rather heavy clay, the other a medium 

 sandy loam. Unquestionably there are numerous other factors than 

 the amount of plant food carried by the two soils which enter into 

 their productiveness; nevertheless, some relationships exist between 

 this question and their requirements for these fertilizer elements. As 

 shown in Table IV, the phosphoric-acid content of both soils is low; 

 until this element has been added in sufficient quantities there can be 

 no increase yields. Although the nitrogen supply in the two soils is 

 found in about the same proportion as the phosphoric acid, it is evidently 

 changed into a more available form faster than the latter element. 



The potash content of the Cecil clay loam is about double that of the 

 Cecil sandy loam, both soils showing that potash is in no way the Hmit- 

 ing element. Indeed, it is doubtful whether this element can be applied 

 to the former at a profit. A glance at Table I, which gives the mineral 

 composition of the Cecil series, shows that in the fine sand and silt 

 separates the potash minerals predominate and that biotite mica is 

 found among the abundant minerals in all five samples. 



