BIOAVAILABILITY OF ZINC, CADMIUM, AND LEAD IN A METAL-CONTAMINATED ALLUVIAL SOIL

Metal mining activities can cause a variety of soil contamination problems including the deposition of sediments having high concentrations of heavy metals on alluvial soils. This study was conducted to investigate the effects of various soil amendments or combinations of amendments on Zn, Cd, and Pb bioavailability in a metal-contaminated alluvial soil as indicated by a chemical fractionation procedure and soybean [Glycine mar (L.) Merr.] growth and heavy metal composition. Total soil concentrations were 1165 mg/kg for Zn, 11 mg/kg for Cd, and 110 mg/kg for Pb, and evidence suggested that Zn phytoxicity was limiting soybean growth. In one greenhouse experiment, the addition of limestone, N-Viro soil, and K2HPO4 significantly increased soybean yields; and the addition of limestone, limestone suspension, cattle manure, poultry litter, N-Viro, and K2HPO4 significantly decreased soybean tissue Zn concentrations as compared to the control. The limestone, limestone suspension, cattle manure, N-Viro, and K2HPO4 amendments also significantly reduced KNO3-extractable Zn as compared to the control. In a second greenhouse experiment, the combination of limestone at 1. 12 or 2.24 Mg/ha and 10 Mg/ha of cattle manure produced significantly higher soybean yields as compared to either amendment alone for the first cutting. For the same cutting, a significant limestone by manure rate interaction was found for concentrations of Zn, Cd, and Pb in soybean tissue and for Zn, Cd, and Pb uptake. Generally, the effects of increasing limestone rate were diminished as the manure rate increased. Root dry weights significantly increased and root tissue Zn concentrations significantly decreased with both rates of limestone application compared to 0 Mg limestone/ha for samples taken at the completion of experiment two. Root tissue Cd or Pb concentrations were not significantly influenced by limestone or manure rates. Significant increases in NaOH-extractable Zn and Pb were found with increasing limestone rates whereas NaOH-extractable Cd significantly decreased. Correlations between soybean tissue Zn concentrations and various Zn fractions and diethylenetriaminepentaacetic acid (DTPA)-extractable Zn indicated significant relationships for KNO3-Zn (r = 0.92), NaOH-Zn (r = 0.62), KNO, + H2O-Zn (r = 0.82), KNO3 + NaOH-Zn (r = 0.88), KNO, + H2O + NaOH-Zn (r = 0.54), and DTPA extractable Zn (r = 0.70).