Aluminum in Soils: VI. Changes in pH-Dependent Acidity, Cation-Exchange Capacity, and Extractable Aluminum with Additions of Lime to Acid Surface Soils
- D. R. Bhumbla and
- E. O. McLean
Surface soils differing in extractable aluminum and organic matter were limed at various rates, moist incubated, and analyzed for pH-dependent acidity by extracting KCl-leached soils with triethanolamine (TEA) buffered BaCl2 solution-pH 8.2. The pH-dependent acidity decreased markedly with rate of liming. Aluminum was extracted with 1n KCl and with 1n NH4OAc-pH 4.8 using varying amounts of solution and extraction times. Increased amounts of KCl solution removed more Al from unlimed soils, and the pH-dependent acidity decreased correspondingly. More Al was extracted with NH4OAc-pH 4.8 than with KCl, and differences in pH-dependent acidity of limed and unlimed soils were relatively less pronounced, especially in soils high in soluble Al. Prolonged leaching with NH4OAc-pH 4.8 reduced these differences more. Cation-exchange capacities (CEC) measured with NH4OAc-pH 7 or with TEA buffered BaCl2-pH 8.2 did not vary appreciably with rate of liming. In soils high in soluble Al, CEC measured by leaching with unbuffered salt solutions were much lower than those obtained with NH4OAc, but increased markedly with liming. The data suggest that acidity measured in KCl-leached soils includes not only the weak acid H+ ions which become reactive or displaceable at higher pH, but also acidity related to organic-complexed Al or hydroxy-Al polymer.
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