ZINC FRACTIONS IN WETLAND RICE SOILS AND THEIR AVAILABILITY TO RICE

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Abstract
A method for fractionation of soil Zn in wetland rice soils is described. The fractionation scheme distinguishes 4 Zn fractions: Zn in soluble organic complexes and exchange positions; Zn in amorphous Fe and Al oxides; Zn in crystalline oxides of Fe and Al; and residual Zn fraction mainly in clay structures. Correlation, multiple linear regression and path-coefficient analyses confirmed that Cu(OAc)2 [copper acetate], ammonium oxalate reagents can partition Zn from the soil matrix that is relevant to plant growth. It is apparent from the path diagram that plant-available Zn is controlled by equilibria involving Zn in soluble organic complexes, exchange positions, and amorphous Fe and Al oxides (r2 = 0.91). Zn measured by Cu(OAc)2 extraction apparently is of major importance in maintaining a Zn level sufficient for rice in wetland soils.