[Effects of soil components on zinc sorption-desorption by microaggregates in a paddy soil in Mingshan River watershed]

By using simulation-incubation test and selective dissolution method, this paper studied the effects of soil components on the zinc sorption-desorption by the microaggregates from a typical paddy soil in Mingshan River watershed. The Zn2+ sorption capacity of bulk soil and microaggregates was significantly correlated with the contents of soil organic matter, free oxide iron, amorphous oxide iron, and cation exchange capacity. Whether or not the soil components were removed, the Zn2+ sorption by the bulk soil and microaggregates fitted well to the Freundlich isotherm model, and the Zn2+ sorption capacity was in the order of <0.002 mm microaggregates >0.25-2 mm microaggregates > bulk soil >0.002-0.053 mm microaggregates >0.053-0.25 mm microaggregates. After the removal of the soil components, the Zn2+ sorption capacity by bulk soil and microaggregates decreased, and the decrement was in the order of <0.002 mm microaggregates > bulk soil >0.053-0.25 mm microaggregates, compared with that before the removal of the soil components. After the removal of organic matter, the decrement of the Zn2+ adsorption capacity of <0.002 mm microaggregates, 0.053-0.25 mm microaggregates, and bulk soil was 39.56% +/- 1.97%, 26.68% +/- 4.21%, and 36.39% +/- 2.31%; after the removal of free oxide iron, the decrement was 30.41% +/- 1.91%, 20.14% +/- 3.33%, and 28.73% +/- 1.22%; and after the removal of amorphous oxide iron, the decrement was 22.12% +/- 1.27%, 12.43% +/- 2.11%, and 20.15% +/- 2.62%, respectively. The decrement of Zn2+ sorption by bulk soil and microaggregates after the removal of the soil components was in the order of removal of organic matter > removal of free oxide iron > removal of amorphous oxide iron, and the difference among the treatments was significant. After the removal of the soil components, the non-specific adsorption of Zn2+ by bulk soil and microaggregates increased significantly, which increased the Zn2+ mobility in soil, while the specific adsorption decreased, resulting in the decrease of the buffering- and retention capability of the bulk soil and microaggregates to Zn2+.