TRACE-METAL CHEMISTRY IN ARID-ZONE FIELD SOILS AMENDED WITH SEWAGE-SLUDGE .4. CORRELATIONS BETWEEN ZINC UPTAKE AND EXTRACTED SOIL ZINC FRACTIONS

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 left bracket KNO//3, H//2O, NaOH, EDTA (ethylene-dinitrilotetraacetic acid), HNO//3, in sequence right bracket 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 KNO//3 and H//2O in sequence is associated with the highly labile, soluble pool, dominated by Zn**2** plus , which determines immediate bioavailability. (ii) Zinc extracted by KNO//3, H//2O, 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) HNO//3-extractable Zn is associated with a nonlabile pool that is not bioavailable.