EFFECTS OF SLUDGE AMENDMENTS ON SOIL CATION EXCHANGE CAPACITY, ORGANIC MATTER, AND SUBSEQUENT HEAVY METAL UPTAKE BY VEGETABLES
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Date
1987-12
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Department
Hood College Biology
Program
Hood College Environmental Biology
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Abstract
Sewage sludge compost or leaf compost was applied to garden vegetable
plots at the rate of 110 metric tons/hectare per year for four consecutive
years to determine the influence of soil amendments on soil cation exchange
capacity and on soil organic matter. The effect of soil amendments on zinc
and cadmium uptake by various species of garden vegetables was also
evaluated in light of changes of these soil properties.
Sludge compost treatments increased soil cation exchange capacity,
whereas leaf compost did not. In contrast, soil organic matter increased
in both leaf compost and sludge compost-treated soil compared to control.
Cadmium and zinc levels in soil increased following sludge treatment, but
applications of leaf compost caused no significant change.
Swiss chard (Beta vulgaris L., cv. Cicla, Fordhook Giant) absorbed
less zinc and cadmium from sludge compost-amended soil compared to control.
Similarly, beet (Beta vulgaris, L., cv. Red Ball) leaves grown in sludge
compost soil showed lower zinc and cadmium content than those grown in
control plots. Metal content of leaves or roots in radish (Raphanus
sativus L.) was not affected by compost-amended soil.
The results indicate that applications of leaf compost increased soil
organic matter, thereby improving soil structure without increasing cadmium
and zinc concentrations. Although sludge compost increased soil heavy
metal concentrations, the concomitant increase in cation exchange capacity
appeared to restrict metal uptake by several vegetables. Additional work
is necessary to determine if sludge applications will cause heavy metal
toxicity to other crops, micro-organisms, and ground water.