19171 SOILS FERTILIZEKS. 625 



cations with reference to their tendency for being adsorbed occurred in the 

 order : Al, K. Ca, Mn, Mg, and Na. The numbers for the ions Ca. Mn, and Mg 

 were very nearly the same. . . . The metals, with the exception of the potas- 

 sium occur in the order of their valence and . . . metals of the same valence 

 give practically the same values. 



" It was found that a soil that had adsorbed large quantities of potassium 

 would give part of this up wlien treated with various salt solutions. In the case 

 of the solutions tried it was found that, with reference to their ability to set 

 free adsorbed potassium, the salts occurred in the following order : AlCU, NH,C1, 

 MnCl2. CaCU, CaSO*. MgCh, NaCl, CaCO». 



" When the soil was treated with a mixture of salts it was found that the 

 iimount of each ion adsorbed was cut down by the presence of the other. The 

 total number of equivalents adsorbed from the mixture was greater, however, 

 than from either of the salts alone." 



Results of soil fertility studies, C. B. Williams (North Carolina Sta. Rpt. 

 1916, pp. 14-16). — Chemical and petrographic studies of the soils of North 

 Carolina have shown that "wide variations in the total amount of the elements 

 of plant food .... exist between the soils of the Appalachian Mountains, Pied- 

 mont plateau, and Atlantic coastal plain. The soils of the first physiographic 

 province are better supplied with phosphoric acid, potash, and lime than are 

 those of the other two proAances. . . . Those of the Piedmont plateau are, as a 

 rule, amply supplied with potash and lime and with phosphoric acid in rather 

 large amounts in some cases. On the other hand, the soils of the coastal plain 

 south of Albemarle Sound are markedly deficient in all essential elements of 

 plant growth. Nitrogen is usually low in a majority of the soils of all three sec- 

 tions of the State." 



Petrographic studies of these soils correlate markedly with the chemical 

 studies. Topography plays an important part in their chemical composition. 

 Soils of the mountains are formed from the same or similar rock as are those 

 of the Piedmont section, but in the mountains the soil mantle is not so well 

 defined, consequently there are more of the minerals found in the parent rock 

 when the superficial covering has been removed. The coastal plain soils are 

 markedly deficient in minerals except quartz. 



In coordinating these studies with the field tests, using various crops as indi- 

 cators for measuring the relative densities of the soil solution, close relationships 

 appear to exist between the chemical and mineral composition of the soils of 

 each province and their requirements for plant nutrients. Nitrogen is either the 

 first or second element required by all the soils under experiment. 



Field tests with four distinct types of soil in the mountain sections, namely, 

 Porter's clay, Porter's loam, Toxaway silty loam, and Toxaway loam, show 

 that with all four types " phosphoric acid is needed first, and potash shows no 

 gain with different crops, except where complete fertilizer is used and large 

 crops produced. Lime alone shows gains on leguminous crops, and when used 

 with complete fertilizer a gain is made. On Porter's clay and Porter's loam 

 nitrogen is second in importance to phosphoric add, and has to be supplied to 

 produce good crops. Toxaway loam and Toxaway silty loam need nitrogen for 

 best results, but not so much as the upland mountain soils to produce remunera- 

 tive crops." 



Field tests of Piedmont soils, Cecil clay near Charlotte, Cecil clay loam near 

 Statesville, and Cecil sandy loam near Gastonia, all show phosphoric acid to 

 be the limiting constituent of plant food, with nitrogen second. Very little 

 benefit is derived from potash, except whei-e used in a complete fertilizer. The 

 tests on the Iredell loam near Charlotte show that nitrogen is the first element 

 of plant food needed, with potash and lime next. Although a complete fertilizer 



