RELEASE OF EXCHANGEABLE SODIUM FROM AN ALKALI SOIL UPON AMENDMENT APPLICATION—ROLE OF VARIABLE CHARGE AND EXCHANGEABLE CATION HYDROLYSIS

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Abstract
In laboratory studies the effect of high pH of alkali soil on its charge characteristics was evaluated. The effect of pH on charge characteristics was studied on one soil with 3 pretreatments: a calcareous soil from which organic matter was removed (A); a soil from which lime and organic matter had been removed (B); and a soil from which lime had been removed treated with an alkali extract of farmyard manure (C). Alkali soil having both high pH and high sodicity contained significant amounts of variable charge. Applying an amendment for reclaiming alkali soils reduced the variable charge component of cation exchange capacity due to decrease in soil pH. For this reason and due to reactions involving hydrolysis of exchangeable Na and double decomposition reaction between Na-soil and CaCO3, the release of Na+ from the exchange complex was more than the equivalent amounts of Ca adsorbed from applied gypsum solutions.