Soil Acidity and Liming: I. Effect of the Extracting Solution Cation and pH on the Removal of Aluminum from Acid Soils

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Abstract
Extractable Al is one criterion used for predicting the lime requirement of acid soils; therefore, a reliable measurement of extractable Al across a broad range of soil properties is desirable. The amount of Al removed from exchange sites may be affected by the exchanging cation and the extracting solution pH. This study was conducted to determine (i) the efficiency of Cu, La, and K, and (ii) the effect of solution pH in removing Al from soils with different organic matter content. Nine soils with an organic matter range of 0 to 58% were successively extracted seven times with Cu2+, La3+, and K+ nonbuffered chloride salt solutions and buffered acetate solutions at three pH values. With the buffered acetate solutions there was no cation effect in the removal of Al from mineral soils, but for organic soils (> 30% organic matter) there was an efficiency order with Cu > La > K. The nonbuffered chloride salts of La and K removed similar amounts of Al from mineral soils, but La removed more Al than did K from organic soils. The Al removed was linearly related to extractant solution pH for organic soils, but did not change appreciably for mineral soils when the solution pH was below pH 4.2.

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