FIELD-STUDY OF AGRICULTURAL USE OF SEWAGE SLUDGE .3. EFFECT ON UPTAKE AND EXTRACTABILITY OF SLUDGE-BORNE METALS

Metal concentrations in soil and plant tissue resulting from land application of liqid digested sewage sludge were examined by determining Cu, Zn, Cd, Ni, and Cr in rye and sorghum-sudan. Forage tissue in corn grain and stover, and DTPA-extractable metals in soil. Four crops were grown successively after the application of up to 60 metric ton/ha (dry solids basis) of liquid sewage sludge on a sandy loam and a silt loam in Wisconsin. In general, the addition of sludge increased the concentrations of Cu, Zn, Cd, and Ni in the vegetative tissue but, except for Zn, the additions had relatively little effect on the metal content of corn grain. Chromium did not accumulate in the tissue or grain. In all cases, concentrations of metals were below levels considered to be toxic to the crops grown. Regression analysis showed that DTPA might be useful as a predictor of metal concentrations in the vegetative portions of the plant. However, the relationships were not the same for different crops.