Effect of Soil Cation Exchange Capacity on the Uptake of Cadmium by Corn

Since many investigators examine the environmental input of sludge-borne heavy metals through studies involving soluble metal salts, it is imperative that the equivalence of these two metal sources be tested. Samples of B1 horizon of the Ava series (Typic Fragiudalfs) and Ap horizon of Maumee series (Typic Haplaquolls) were separately diluted with samples of the Plainfield series (Typic Udipsamments) to obtain soil mixtures having cation exchange capacities (CEC) of about 5.3, 10.6, and 15.9 meq/100 g. A mixture containing equal proportions of Ava and Maumee were also diluted with Plainfield to give an equivalent range of CEC. One portion of each of the nine experimental soils was admixed with the equivalent of 100 metric tons/ha of dried, digested sewage sludge to provide soil-Cd concentrations of 10 mg/kg. The remaining portion was treated with CdCl₂ at rates to provide equivalent soil-Cd concentrations. Corn (Zea mays L.) (single-cross Mo17 × H98), selected for its inherited capacity to take up relatively high amounts of Cd, was planted in four pots of each mixture. Three plants were harvested at the end of 3 weeks and an additional three after 7 weeks. Cadmium uptake and dry weight production were affected to the greatest extent by Cd source > soil or soil mixture > CEC. Cadmium uptake and plant yields were inversely related to CEC on CdCl₂-treated soil but were not significantly different on soil mixtures treated with sludge. Less cadmium was taken up from soil mixtures that contained increasing quantities of Maumee, but there was no evidence that organic matter decreased cadmium uptake beyond that attributable to increased CEC. Total amounts of cadmium accumulated per plant were significantly different on sludge-treated mixtures, but the magnitude of the differences were small compared to those from CdCl₂-treated soils. Biomass produced during the interval between the first and second harvest contained less cadmium than that collected during the first harvest. For the most extreme example (Ava B1 treated with CdCl₂), only slightly more than 2% of the total soil cadmium was depleted by corn plants during 7 weeks of growth.