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Influence of pH, Phosphorus, Cadmium, Sewage Sludge, and Incubation Time on the Solubility and Plant Uptake of Cadmium¹

ABSTRACT

Corn (Zea mays L.) ‘Pioneer-3932A’ was grown in the greenhouse on a loamy sand amended with cadmium, cadmium-spiked sewage sludge, and sewage sludge. Soil pH was adjusted to approximately 5.7, 6.7, and 7.8, and phosphorus was applied at 0, 200, and 400 µg/g soil. Soil treatments were applied 0, 8, and 16 weeks prior to planting, and the plants were grown for 5 weeks.

Increasing the pH of the soil amended with inorganic cadmium (CdSO₄) decreased the Cd concentration of corn seedlings by approximately 67%. The Cd concentration was reduced approximately 47% for a similar increase in pH on soil amended with Cd-spiked sludge.

The Cd concentration of corn seedlings was significantly reduced by the addition of P. Increasing incubation time decreased the availability of added inorganic Cd, but increased the availability of Cd applied with sewage sludge.

Increasing the amount of Cd added to the soils increased the Cd concentration of the corn seedlings regardless of the form of Cd used. Cadmium concentrations in the corn seedlings were significantly correlated with DTPA-extractable soil Cd.

Solubility measurements of Cd in the acidified soils showed undersaturation with respect to all known Cd minerals, whereas in soils above pH 7.25 the Cd solubility was limited by CdCO₃ at a CO₂ level of 0.003 atm or higher and showed the expected hundredfold decrease in solubility for each unit increase in pH. The minerals Cd₃(PO₄)₂ and Cd(OH)₂ are much too soluble to account for the precipitation of Cd in these soils.

Key Words: interactions • DTPA • Zea mays L. • heavy metals • solid-phase

¹ Contribution from the Dep. of Agronomy, Colorado State Univ. Exp. Stn., Fort Collins, CO 80522, and published as Sci. Ser. Pap. no. 3395.

² Assistant Professor of Soils, Soil Science Dep., Univ. of Florida, and Professors of Agronomy, Colorado State Univ., Fort Collins, respectively.

Received for publication July 5, 1977.