SOIL FACTORS AFFECTING PLANT CONCENTRATIONS OF CADMIUM, COPPER, AND ZINC ON SLUDGE-AMENDED SOILS

Establishment of maximum cumulative metal loading rates of sludge requ ire 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 a pplication were evaluated, Swiss chard (Bera vulgaris L.) and lettuce (Lactuca sativa L.) were planted on five fields (Typic Hapludults) wit h known sludge disposal history, After harvest, tobacco (Nicotina taba cum L.) following swiss chard and peanut (Arachis hypogea L.) followin g 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, a nd pH were determined on a composite 20-cm depth soil sample and Mehli ch-3 extractable metals were determined by Ij-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 short ly after anthesis (tobacco and peanut), Simple linear regressions were poor between plant metal concentration and soil-extractable metal fbr all extractants, Inclusion of soil properties in the best-tit multiva riate regression models improved the relationship for metal concentrat ion in plants. Values for R-2 ranged from 0.30 to 0.96 with the poores t correlations obtained for Cu in lettuce and peanut, Best-fit models for all other crop-extractant-metal combinations had R-2 > 0.83. Metal s extracted by the three extractants were correlated with each other s o their inclusion in models describing plant concentrations of heavy m etal in this study gave similar results.