CD AND ZN PHYTOAVAILABILITY OF A FIELD-STABILIZED SLUDGE-TREATED SOIL

Phosphorus (at rates equivalent to 0, 100, 200, 300, and 400 kg P ha-15 cm-1) ha and N (at rates equivalent to 0 and 200 kg N ha-15 cm-1) were added to a sludge-treated soil obtained from an experimental field. The P- and N-treated soils were packed in containers and used to grow Swiss chard (Beta vulgaris) in a glasshouse. Concentrations and activities of Cd2+ and Zn2+ ions and the distribution of Cd and Zn complexes in the soil saturation extracts were determined. Results indicated that P additions up to 400 kg ha-15 cm-1 did not affect the yield of or the Cd and Zn uptake by Swiss chard grown on this sludge-treated soil. The yield of Swiss chard grown on the soil treated with 200 kg N ha-15 cm-1 was significantly greater than that of the control. The Cd and Zn uptake by Swiss chard, however, did not increase in proportion with the yield increment. With the increased yield, the uptake of Cd was increased by 50%, but the uptake of Zn remained unchanged. Potassium, PO4, and NO3 concentrations in soil saturation extracts increased with amounts of P and N added as both were added as K salts. Total Cd and Zn concentrations, Cd and Zn activities, and overall distribution of Cd and Zn complexes of the soil saturation extracts, however, were not significantly affected by P and N treatments. The plant uptake of Cd and Zn in this sludge-treated soil was probably limited by the rate of Cd and Zn desorption from solid phase.