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Trace Metal Chemistry in Arid-Zone Field Soils Amended with Sewage Sludge: III. Effect of Time on the Extraction of Trace Metals¹

ABSTRACT

The surface horizons of two arid-zone field soils that either had received amendments of composted sewage sludge annually since 1975, or had received amendments of liquid sludge between 1976 and 1978, were fractionated by sequential extraction for 4 years annually, beginning in 1979, to compare the solid-phase forms of Ni, Cu, Zn, Cd, and Pb. The total concentration of each trace metal in the soils continually receiving composted sludge increased with time, whereas the total concentration of the metals in the soil that had received liquid sludge until 1978 did not increase with time. Regardless of the time variation of total metal concentration, the percentages of the metals in either the EDTA (ethylenedinitrilote-traacetic acid)-extractable fraction or the HNO₃-extractable fraction often tended to increase with time in the soils. This trend was more evident in the lighter-textured field soil receiving composted sludge. It was concluded that the observed increase in EDTA-extractable trace metals with time could be the result of the formation of trace metal carbonates accompanying the gradual mineralization of the organic matter in the applied sludge in the soil environment.

¹ Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521.

² Professor of Soil Science, Research Associate II, Graduate Research Assistant, and Professor of Agricultural Engineering, respectively.

Received for publication June 8, 1982. Accepted for publication May 9, 1983.