Soil factors affecting plant concentrations of cadmium, copper, and zinc on sludge-amended soils

Establishment of maximum cumulative metal loading rates of sludge require metals in soils be related to metal concentrations in plants grown on those soils. The relationship between plant concentrations of Cd, Cu, and Zn and soil properties on sites of long-term municipal sludge application were evaluated. Swiss chard (Beta vulgaris L.) and lettuce (Lactuca sativa L.) were planted on five fields (Typic Hapludults) with known sludge disposal history. After harvest, tobacco (Nicotiana tabacum L.) following swiss chard and peanut (Arachis hypogea L.) following lettuce were planted in the same plots. Extractable Cd, Cu, and Zn (Mehlich-3, 0.05 M DTPA, 0.05 M EDTA), clay, humic matter, organic C, and pH were determined on a composite 20-cm depth soil sample and Mehlich-3 extractable metals were determined by 15-cm increments on a 60-cm depth sample from each plot. Tissue concentrations of Cd, Cu, and Zn were measured near harvest maturity (swiss chard and lettuce) or shortly after anthesis (tobacco and peanut). Simple linear regressions were poor between plant metal concentration and soil-extractable metal for all extractants. Inclusion of soil properties in the best-fit multivariate regression models improved the relationship for metal concentration in plants. Values for R2 ranged from 0.30 to 0.96 with the poorest correlations obtained for Cu in lettuce and peanut. Best-fit models for all other crop-extractant-metal combinations had R2 0.83. Metals extracted by the three extractants were correlated with each other so their inclusion in models describing plant concentrations of heavy metal in this study gave similar results