ALFALFA GROWTH AND ABSORPTION OF CADMIUM AND ZINC FROM SOILS AMENDED WITH SEWAGE-SLUDGE

Safe application of sewage sludge to soil used for food chain crops re quires careful management of the heavy metals that pose a potential he alth hazard. Soils in pots were amended with various chemicals and sew age sludge. Alfalfa (Medicago sativa L.) was grown in the amended soil s to measure yield and shoot concentrations of Cd and Zn. The four soi ls were a strongly calcareous Millville silt loam (Typic Haploxeroll), a slightly calcareous Kidman loam (Typic Haplustoll), a slightly acid ic Sinks silt loam (Cumulic Cryoboroll), and an acidic Franklin Basin silt loam (Pachic Paleboroll). Soils were amended with 20 Mg ha-1 dry weight of sewage sludge; some soil samples also received additions of CaCl2, CaO, CaCO3, or HCl. Pots were set on benches outside after alfa lfa germinated. Adding 20 Mg ha-1 sludge provided 4.6 kg ha-1 Cd, whic h exceeds the proposed US EPA criteria maximum of 0.5 kg Cd ha-1 per y ear. Alfalfa was grown on all soils and was harvested three times. The Cd concentrations in dry alfalfa tops ranged from 0.21 mg kg-1 for co ntrols to 0.64 mg kg-1 for sludge-amended soils. Neither Cd nor Zn rea ched phytotoxic concentrations in the alfalfa. In most treatments Cd l evels in alfalfa equalled or exceeded the 0.5 Cd kg-1 that is permissi ble in animal feed. During the rapid growing period between the first and second cuttings, Cd and Zn concentrations in alfalfa were as much as 50% lower than concentrations during periods of slower growth. The total Cd and Zn recovered in alfalfa grown on the two slightly acidic soils was about 35-50% higher than from the non-acid soils. Adding lim e to the acid soils significantly reduced Cd and Zn concentrations in tissues.