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Trace Metal Chemistry in Arid-Zone Field Soils Amended with Sewage Sludge: IV. Correlations Between Zinc Uptake and Extracted Soil Zinc Fractions¹

ABSTRACT

The surface horizons of two field soils that had been amended with composted or liquid sewage sludge for 3 to 6 y were extracted with a series of reagents [KNO₃, H₂O, NaOH, EDTA (ethylenedinitrilotetraacetic acid), HNO₃, in sequence] and with DTPA (1,4,7-triazaheptane-1,1,7,7-pentaacetic acid) to characterize the zinc (Zn) pool in the soils with respect to lability and bioavailability. Statistical correlation analysis, comparing the extracted Zn fractions with the concentration of Zn in the leaves of barley (Hordeum vulgare L.) grown on the two soils, led to the following conclusions: (i) Zinc extracted by KNO₃ and H₂O in sequence is associated with the highly labile, soluble pool, dominated by Zn²⁺, which determines immediate bioavailability. (ii) Zinc extracted by KNO₃, H₂O, and NaOH in sequence has a strong, positive, 1:1 correlation with DTPA-extractable Zn and, therefore, is associated with the labile, plant-available Zn pool. (iii) EDTA-extractable Zn represents a reservoir of potentially bioavailable Zn, and (iv) HNO₃-extractable Zn is associated with a nonlabile pool that is not bioavailable. These general relationships between extracted Zn fractions and bioavailability were applicable to both soils investigated and did not depend on the type of sludge applied or the length of time of sludge application.

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

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

Received for publication October 24, 1983. Accepted for publication December 22, 1983.