A greenhouse experiment is reported which was designed to evaluate possible detrimental effects due to high loadings of waste water sludge from four Wisconsin municipalities. The sludges were selected because of abnormally high concentrations of Zn, Cu, Cr, or Ni, and were mixed, after being air-dried, with a limed (pH 6.8) sandy loam soil at rates from 63 to 502 metric tons/ha (oven-dry solids basis). The soils then were leached to remove soluble salts. Three crops [corn (Zea mays L.), rye (Seceale cereale L.), and corn] were then grown in succession on the sludge-amended soils. Soil solution conductivity and soil pH were monitored at each cropping, and vegetative yield and tissue concentration of Cd, Cr, Cu, Mn, Ni, and Zn determined.
One of the sludges was a high lime (pH 7.8) material, and this sludge raised soil pH to 7.4. At the high rates, the other sludges lowered pH somewhat. Also, soluble salts reached sufficient concentration at the higher rates to be detrimental to yield of the first corn crop. Significant positive yield responses, due to N, P, and K added by the sludges, occurred up to the 125 metric ton/ha rate. On all but the high pH sludge, crop yields were depressed at the high rate. The tissue concentration of metals increased with sludge rate, and significant differences between sludges were found with respect to tissue metal concentrations. Phytotoxic concentrations of Cu occurred most often. On the average, the tissue concentrations of the control were Cd, 0.4; Cr, 1.4; Cu, 7.4; Mn, 33; Ni, 1.7; and Zn, 38 ppm whereas at the 502 metric ton/ha rate of sewage sludge the values were Cd, 5; Cr, 6; Cu, 23; Mn, 346; Ni, 16; and Zn, 289 ppm.