Zinc speciation in phosphate-affected soils

Zinc (Zn) speciation was determined in a Zn pre-treated Andosol, Inceptisol, and a Vertisol before and after adding phosphate. The fractions obtained, i.e., soluble, exchangeable, iron-manganese (Fe-Mn) bound, chelated and insoluble organic forms had a different distribution in the three soils. The exchangeable form predominated in the Andosol, followed by Fe-Mn oxide bound Zn and minor amounts of the chelated forms, whereas Fe-Mn oxide bound Zn was very abundant in the Inceptisol and Vertisol. Sizable amounts of the exchangeable form were also present. Phosphate pre-treatment of the Inceptisol and Vertisol did not alter the distribution of the different forms of Zn, whereas in the Andosol the exchangeable as well as the Fe-Mn oxide bound Zn increased markedly, chelated Zn also increased somewhat.