Rw. Miller et al., ALFALFA GROWTH AND ABSORPTION OF CADMIUM AND ZINC FROM SOILS AMENDED WITH SEWAGE-SLUDGE, Agriculture, ecosystems & environment, 53(2), 1995, pp. 179-184
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.