Abstract
The suitability of two composted solid urban wastes for crop production was evaluated in a pot experiment with sorghum (Sorghum bicolor) that focused on the geochemical fractions, bioavailability, and phytotoxicity of copper (Cu), manganese (Mn), and zinc (Zn). Total concentrations of Cu, Mn, and Zn in soil increased with increasing waste application, ranging from 1.6 to 48.2 mg kg−1 for Cu, 84 to 474 mg kg−1 for Mn, and 13.8 to 597 mg kg−1 for Zn. Waste application significantly increased pH and electrical conductivity (EC) of the soil. Copper, Mn, and Zn in the waste-amended soil were speciated into mobile (F1), easily mobilizable (F2), occluded in Mn oxides (F3), organically bound (F4), occluded in amorphous Fe oxides (F5), occluded in crystalline Fe oxides (F6), and residual (F7) fractions to assess the lability of the metals. On the average, the F4 was the most dominant Cu and Zn fraction, accounting for between 37 and 60% of total Cu and from 14 to 40% of total Zn concentrations, whereas F3 was the dominant Mn fraction closely followed by F4. The concentrations of Cu, Mn, and Zn in sorghum dry matter (DM) decreased with increasing waste application, probably induced by osmotic stress and ionic toxicity. Tissue Zn (Y-Zn) and Mn (Y-Mn) correlated significantly with the F1 and F2 fractions, but pH was an overriding factor in predicting Cu and Zn bioconcentration. Used as soil amendments, the application rate for these Zaria urban wastes should be limited to ≤10% (w/w basis), as Zn in the sorghum tissue reached the toxic limit just from one application of the waste to soil.
Published Version
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