Availability and distribution of heavy metals, nitrogen, and phosphorus from sewage sludge in the plant-soil-water continuum

TR Number
Journal Title
Journal ISSN
Volume Title
Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University

Research was conducted during 1984 and 1985 to determine Cd, Cu, N, Ni, P, and Zn availabilities to barley (Hordeum vulgare L.) and corn (lea mays L.) grown on four sludge-amended soils. Field studies were conducted on Acredale silt loam (Typic Ochraqualf), Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodie Paleudult), and Groseclose silt loam (Typic Hapludult). An aerobically digested sewage sludge, which was dewatered for approximately 2 years on sandbeds, was obtained from a sewage treatment plant with major industrial inputs. In the spring of 1984, this sludge was applied at rates of 0, 42, and 84 dry Mg ha- 1 to the poorly drained Acredale soil and at rates of 0, 42, 84, 126, 168, and 210 dry Mg ha - 1 to the well-drained Bojac, Davidson, and Groseclose soils. The 210 dry Mg ha-1 sludge rate supplied 4.5 kg Cd, 750 kg Cu, 3350 kg N, 43 kg Ni, 6900 kg P, and 600 kg Zn ha - 1. A 14-day anaerobic N incubation study indicated that mineralization of sludge organic N varied from 9.2% at the 42 Mg ha - 1 sludge rate to 4.2% at the 210 Mg ha - 1 rate. Th is relatively low percentage of N mineralized from the sludge may reflect the inhibitory effects of the high sludge metal levels on N transformations and the changes in sludge composition during long-term dewatering on sandbeds. Sludge application increased crop yields, except where the amounts of N mineralized from the sludge was inadequate to supply the N requirement of the crop.

Crop yields were not decreased by either metal phytotoxicity or P deficiency on the four sludge-amended soils. On the three well-drained soils, Cu and Zn phytotoxicity did not occur where these metals were applied in excess of US EPA guidelines of 280 kg Cu and 560 kg Zn ha- 1. Although there were increases in Cd, Cu, Ni, and Zn in plants grown on the sludge-amended soils, the metal concentrations were within the ranges of those reported for nonsludged soils. Levels of DTPA-extractable metals in the Ap horizon of the soils provided a good indication of the amounts of metals in the soils from sludge application. Relatively low correlations occurred between DTPA-extractable Cd, Cu, Ni, and Zn and the respective metal concentrations in plant tissue. These low correlations were attributed to the small increases in metal concentrations in tissue from metals supplied by sludge application. The DTPA-extractable Cd, Cu, Ni, and Zn concentrations in soils sampled from various depths indicated no downward movement of these metals in the sludge-amended soils, except for virtually negligible downward movement of Cu in the Groseclose soil. Dilute double-acid extractable P in these samples indicated a small amount of P movement in only the sludge-amended Bojac and Davidson soils. The limited N mineralization of the sludge under study substantially reduced the potential for NQ3- contamination of groundwater.