THE EFFECT OF SULFATE ON THE AVAILABILITY OF CADMIUM1

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Abstract
The objective of the study was to determine the effect of sulfate salinity on the availability of Cd in soil. Specifically the study consisted of a greenhouse experiment with Swiss chard (Beta vulgaris Cicla) as the biological indicator of Cd in two sets of an acid soil treated with 0.25, 1.00, and 2.50 mg Cd kg−1 in combination with four rates of Na2SO4 ranging up to 30 mol m−3 in the saturation extract (H2O). One set was limed with CaCO3; the other was left as an acid soil. The content of Cd in shoots of Swiss chard after 9 wk postemergence was taken as the measure of available Cd. Immediately after the plants were harvested, the soil solution was analyzed for cations and anions; these data were taken as input data to chemically speciate Cd in the soil solution. The total concentration of Cd in soil solution, CdT, was found to consist of principally Cd2+, CdCl+, and CdSO4° in the unlimed soil. The speciation of the soil solution for the limed soil show CdT to comprise the above plus CdCO3+. Regression analysis of leaf Cd in relation to CdT, Cd2+, acd2+, CdCl+, CdSO4°, and CdCO3° showed leaf Cd to be primarily a function of the aCd2+ in the acid series and CdT in the alkaline series. The availability of soil solution Cd as judged by the Cd concentration of Swiss chard (shoot) was substantially greater for the unlimed soil.