A Field Study of the Agricultural Use of Sewage Sludge: III. Effect on Uptake and Extractability of Sludge-Borne Metals
1977
Kelling, K. A. | Keeney, D. R. | Walsh, L. M. | Ryan, J. A.
Metal concentrations in soil and plant tissue resulting from land application of liquid digested sewage sludge were examined by determining Cu, Zn, Cd, Ni, and Cr in rye (Secale cereale L.) and sorghum-sudan (Sorghum bicolor L. Moench × S. sudanese P. Stapf.) forage tissue, in corn (Zea mays L.) 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. Total recovery of added metals by the four crops was < 1% for Cu, Cd, Ni, and Cr, and 1 to 3% for Zn. Levels of DTPA-extractable Cu, Zn, Cd, and Ni, but not Cr, increased with sludge treatment. 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. The decreases in metal concentrations in the plant tissue and in DTPA extracts with successive crops indicated reversion to less available forms for Zn, Cd, and possibly Ni. The ratio of Cd:Zn in the tissue was about one-third that of the sludge for all crops.
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