Total and labile zinc concentrations in water extracts of rhizosphere and bulk soils of oats and rice

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Abstract
A greenhouse experiment using three soils of different pH levels (4.37 5.78, 6.44) was conducted to determine the effects of rhizosphere on pH, total Zn and labile Zn in water extracts of soils grown to oats and rice. Zn concentrations were determined using a linear sweep cathodic stripping voltammetry technique. In oats, the pH and labile Zn in water extracts were lower in the rhizosphere than the bulk soil and there was no difference in total Zn in water extracts between these two soil zones. Consistently, rhizosphere pH was lower than bulk soil pH with rice but total and labile Zn in water extracts were not statistically different. Zn concentrations (both total and labile forms) in water extracts varied inversely with pH; however, rhizosphere pH changes did not always explain observed differences in extractable Zn.