Differential Accumulations of Cadmium and Zinc by Corn Hybrids Grown on Soil Amended with Sewage Sludge

Researchers have recognized that different varieties and cultivars of plants subjected to the same growing conditions frequently take up different amounts of essential and nonessential trace elements. Differences in uptake appear to be predisposed genetically. In designing studies to determine the nature of the inherited capacity of corn (Zea mays L.) to control the uptake of heavy metals some additional information was needed. The objectives of this study were to determine the extent to which Cd uptake was affected by the proximity of growing plants, whether or not maternal effects were present and the extent to which uptake patterns varied from year to year under normal field conditions. Where corn inbreds known to accumulate relatively high amounts of Cd in leaves and grain were paired with those that took up low amounts in pots of Ipava silt loam (Aquic Argiudoll, fine, montmorillonitic, mesic, pH 5.5) containing 57 mg Cd/kg and 864 mg Zn/kg, supplied as constituents of sewage sludge, the uptake of Cd by individual inbreds was not altered. Using the same soil, reciprocal crosses of corn inbreds that accumulated high and low amounts of either Cd or Zn were grown for 6 weeks in pots. Regardless of which inbred was used as the female parent, concentrations of metals in leaves were not significantly different. Two hybrids, differing only in their capacities to accumulate Cd, were grown in a field study for 3 consecutive years on replicated control and sewage sludge-amended split plots. Initial annual applications of sludge were made 9 years prior to the study and were continued throughout the 3 years. At the beginning, where maximum rates of sludge had been applied, the soil surface contained 28 mg Cd/kg and during the study 31 kg/ha of sludge-borne Cd were applied. Cadmium and Zn concentrations in leaves, grain, and stover from both hybrids were increased each year by increasingly higher applications of sludge, except in grain from the hybrid selected to take up low amounts of Cd. During the last year, grain from the low-Cd accumulator grown on maximum-sludge-treated plots had Cd concentrations that were not significantly different than those in grain from the high-Cd accumulator grown on control plots. Grain-Cd concentrations for the high-Cd accumulator were 13 to 18 times higher than for the low-Cd accumulator when they were grown together on maximum-sludge-treated plots. Accumulative sludge applications did not cause increased Cd concentrations in grain from either of the two hybrids, but did cause increased levels of both Zn and Cd in leaves and stover of the high Cd accumulator. Phytotoxicity symptoms were not observed, even though concentrations of Cd ranged from 20 to 42 and 1.5 to 1.8 mg/kg in the leaves and grain, respectively, of the high accumulator grown on plots treated with maximum amounts of sludge.