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-Ieached soils with triethanolamine (TEA) buffered BaCIa solution-pH 8.2. The pH-dependent acidity decreased markedly with rate of liming. Aluminum was extracted with IN KC1 and with IN NHiOAc-pH 4.8 using varying amounts of solution and extraction times. Increased amounts of KC1 solution removed more Al from unlimed soils, and the pH-dependent acidity decreased correspondingly. More Al was extracted with NH 4 OAc-pH 4.8 than with KC1, 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 NHiOAc-pH 4.8 reduced these differences more. Cationexchange capacities (CEC) measured with NH 4 OAc-pH 7 or with TEA buffered BaCl 2 -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 NH 4 OAc, 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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SUMMARYParagrass, wheat, barley, gram, lady's finger, and dhaincha were grown in a soll whose ESP had been adjusted to 1.7, 30.2, 41.4, 58.4, and 77.9. The growth in terms of dry weight of tops and roots decreased with increasing levels of exchangeable sodium percentage (ESP). The sodium-tolerance index was the highest in paragrass (lower-root CEC) followed by barley and wheat (medium root CEC). Dhaincha, gram, and lady's finger (high root CEC) were relatively sensitive crops having low sodium-tolerance index. Fifty per cent reduction in the yield of wheat, barley, paragrass, lady's finger, dhaincha and gram occurred when ESP was 41, 43, 55, 35, 37, and 36, respectively. Increasing ESP of the soll was associated with increasing Na and decreasing Ca, Mg, and K contents of the tops and roots.
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