A greenhouse experiment was conducted to evaluate yield and the concentration of Cd, Cu, Cr, Ni, and Zn in corn ( Zea mays L.) and rye ( Seceale cereal L.) tissue when grown on a soil limed to pH 6.8 and treated with a waste water sludge that had been amended with Cu, Cr, Ni, and Zn salts. Three rates of each metal in all combinations were used. The rates were obtained by adding the appropriate amounts of each metal to a bulk sample of anaerobic digested sludge. After equilibration for 2 weeks, the sludge was air‐dried, and mixed with a sandy loam soil at the rate of 63 metric tons/ha (solids). Corn, rye, and corn, in that order, were grown on the soil for 6 weeks each. Yields decreased as the Cu and Zn concentration of the sludge increased, while Ni had no appreciable effect. Yields were increased significantly as the sludge Cr concentration increased, indicating that Cr may be inhibiting the uptake or translocation of other metals. This was substantiated by tissue analysis which showed that with increasing sludge Cr, tissue concentrations of the other metals decreased. Tissue concentrations of Cu and Zn were consistently >20 and 400 ppm, respectively, and thus were in the range considered toxic to plants. As the sludge concentration of Cu or Zn increased, tissue concentrations of the other metals were increased, and evidence of Cu‐Zn interactions on plant growth and metal concentrations was obtained. The only Cd sources were that in the soil and in the original sludges, yet the Cd concentration of plant tissue increased with increasing Cu concentration. Yield reductions relative to the control were less and tissue concentrations of the metals decreased from the first to the second corn crop, indicating reversion of the metals to less available form with time.
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Cunningham et al. (1975) studied this question.