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ABSTRACT
Sludge from a swine manure lagoon and municipal sewage sludge were used in a greenhouse study to determine their effects on fescuegrass (Festuca arundinacea Schreb.) yield, heavy metal concentrations, and N uptake. Four variables were used in the experiment: sludge (swine and municipal), soil (loamy sand and sandy clay loam), application method (surface applied and incorporated), and application rate (10, 20, and 40 kg/ha of sludge-applied Cu). Inorganic fertilizer treatments supplying 50, 100, and 200 kg N/ha were also included.
The sludges were applied at the beginning of the experimental period and increased yields for a period of 35 weeks (five harvests), municipal sludge generally resulted in higher yields than did swine sludge during this period. Total recovery of applied N in harvested grass was 24% of the municipal-sludge N and 16% of the swine-sludge N for the first five harvests. Surface application resulted in greater N recovery (24%) than did incorporation (16%, average of both sludges).
Copper concentration in the grass was not affected by sludge type or soil type, but Zn concentrations were higher with municipal sludge and with the sandy clay loam. With municipal sludge the effects of soil types on the concentrations of the other metals in the grass were: Cr and Pb, no effect; Ni, higher with loamy sand; and Cd, initially higher with sandy clay loam, later higher with loamy sand. Surface-applied sludge generally resulted in higher concentrations of metals in the grass than did incorporated sludge. A comparison of the effects of surface-applied and incorporated sludge vs. the effect of chemical fertilizer on metal concentrations in the grass showed: Cr and Pb, no effect; Cu, slight increase due to sludge at first harvest only; and Zn, Ni, and Cd, increase due to sludge.
Heavy metal concentrations in the grass were not consistently related to the soil type. Since the soils differed in cation exchange capacity (CEC, loamy sand, 3.9 meq/100 g; sandy clay loam, 8.5 meq/100 g), it appears that a better criterion than CEC is needed for determining acceptable metal loading rates for major soils of the southeastern United States.
Key Words: Cd • Cu • Cr • Ni • Pb • Zn • cation exchange capacity
1 Paper no. 6507 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh, NC 27650.
2 Assistant Professor, Dep. of Soil Science, North Carolina State Univ., Raleigh.
Received for publication July 26, 1980.
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