Metal Availability in Sludge‐amended Soils with Elevated Metal Levels

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Abstract
Field studies were conducted in 1984 with in situ controlled lateral flow plots to determine Cd, Cu, Ni, and Zn availabilities for corn (Zea mays L.) grown on sludge‐amended soils. These plots were constructed in Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodic Paleudult), and Groseclose silt loam (Typic Hapludult) located in the Coastal Plain, Piedmont, and Ridge and Valley provinces of Virginia, respectively. An aerobically digested sludge from a wastewater treatment plant with major industrial inputs was applied to the soils at rates of 0, 42, 84, 126, 168, and 210 dry Mg ha−1. The highest sludge rate supplied 4.5 kg Cd, 760 kg Cu, 43 kg Ni, and 620 kg Zn ha−1. Corn grain and stover yields at the three locations increased linearly as a function of increased rate of sludge application (r2 ≥ 0.92**, significant at the 0.01 level). Metal concentrations in corn grain and earleaves from all treatments on the three soils were within normal levels. Nonsignificant relationships occurred between levels of DTPA‐extractable Cd, Cu, Ni, and Zn and the respective metal concentration in corn earleaves for data combined over the three soils. Amounts of DTPA‐extractable Cd, Cu, Ni, and Zn in the Ap horizon of the three soils increased linearly (r2 = 0.76** to 0.88**) with rate of sludge application. Maximum DTPA‐extractable metal levels in the soils were 0.6 mg Cd, 150 mg Cu, 4.0 mg Ni, and 75 mg Zn kg−1. The order of DTPA‐extractable metal concentrations in the soils, Cu > Zn > Ni > Cd, paralleled the amounts of metals applied via sludge application. Phytotoxicity did not occur in the corn grown on these diverse soils, even where Cu and Zn were applied in excess of USEPA guidelines.