DECREASE IN AVAILABILITY OF ZINC AND COPPER IN ACIDIC TO NEAR NEUTRAL SOILS ON SUBMERGENCE1

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Abstract
We investigated in the laboratory the changes in the diethylenetriaminepenataacetic acid (DTPA)-extractable Zn and Cu in 26 acidic to near neutral allubial soils on submergence and observed that there was always a decrease in their contents. The percentage of decrease was significantly correlated with initial pH, organic C, clay, cation exchange capacity (CEC), and initial DTPA-extractable contents. The pH seemed to play the most important role in influencing the magnitude of decrease. Multiple regression equations showed that 40.06 and 39.44% variability in the magnitude of decrease of Zn and Cu, respectively, could be accounted for by some of the initial soil properties. On submergence, there was an increase in pH, CO3, S2-, and DTPA-extractable Fe and Mn. The percentage of decrease in DTPA-extractable Zn and Cu was positively correlated with the magnitude of increase in pH (not with Cu), CO32-, S2-, and Fe and was negatively correlated with Mn. Of the variability in the percentage of decrease in Zn and Cu, 57.30 and 59.30% could be accounted for by the change in these parameters, thus lending support to the hypothesis that the decrease in availability of Zn and Cu in acidic in near neutral soils on submergence is due to their precipitation as hydoxide, carbonate, sulfide, and iron compounds. The results of path coefficient analysis revealed that increase in pH directly contributed 36.96% of the percentage of decrease in DTPA-extractable Zn soil on submergence. The total contribution of pH, comprising both direct andindirect effects through CO32-, S2-, and Fe, was 56.4%, suggesting that mechanisms other than those mentioned are operative to cause decrease in Zn availability in soils on submergence. Further research in necessary for their elucidation.
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