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Application of Sewage Sludge to Soils High in Organic Matter¹

ABSTRACT

In a greenhouse study corn (Zea mays L.) was grown in four soils (1.4, 19, 38, and 72% organic matter) that received sewage sludge from Philadelphia, Pa., (PS) at rates to supply 0, 2, 4, and 8 kg Cd/ha. Corn and soybeans (Glycine max. L.) were grown in 1.4 and 19% organic matter (OM) soils that received sewage sludge from Wilmington, N.C., (WS) at rates to supply 0, 2, 4, and 6 kg Cd/ha. The pH of the 1.4% OM soil was adjusted to 6.5 with CaCO₃. The higher OM-content soils received recommended rates of CaCO₃ to increase the pH to 5.0–5.5, the desired range for crop production on these soils. Actual resulting pH values were 5.5, 4.9, and 4.6 for the 19, 38, and 72% OM soils respectively.

Corn yields were depressed by PS but enhanced by WS. Soybean yield was enhanced by WS on the 19% OM soil but depressed on the 1.4% OM soils. Both sludges caused increases in concentrations of Cd, Cu, and Zn in the plant tissue, but concentrations were not high enough to be responsible for the observed yield depressions. The PS was more effective in raising Cd and Zn concentrations in plant tissues than was WS. The type of soil had a varying effect on metal concentrations in the plants. The expected reduction in heavy metal uptake with higher soil OM content was confounded by the low pH of the soils with high OM content. The large quantity of OM added via WS masked the effect of soil OM.

Since the bulk densities of the soils varied from 0.45 to 1.35 g/cm³, regression equations describing Cd concentration in corn stover as a function of OM and cation exchange capacity (CEC) were more precise when OM and CEC were expressed on a volume basis and when OM was determined by a procedure designed to estimate humus rather than total oxidizable OM.

Key Words: cadmium • copper • zinc • nickel • Zea mays L. • Glycine max L. • cation exchange capacity

¹ Paper no. 8101 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh.

² Assistant Professor and former Graduate Research Assistant, Dep. of Soil Science, North Carolina State University, Raleigh, NC 27650.

Received for publication November 23, 1981.