Abstract
The vertical distribution patterns of the major and trace elements in the paddy soils derived from weathered volcanic ashes (Kanto loam) were investigated to estimate the relative mobilities of the elements in the paddy environment. The mobilities were evaluated in terms of the ratios of elemental concetration in paddy soil to elemental concentration in Kanto loam, using Al as a reference element. The elements studied were classified into 3 groups: immobile, mobile and anthropogenic elements. Immobile elements, represented by Cu, Cr, V, Li, Sc, La and Sm, are either captured by the minerals resistant to weathering or strongly adsorbed on soil organic matter and/or clay minerals. Mobile elements are exemplified by Fe, Mn, Co and Ni. Their mobilization is due to the reduction and solubilization of insoluble oxides under reducing conditions, and can be described as a function of ionic radius of solubilized divalent ions. Anthropogenic elements include P, As and Zn, which are characteristically enriched in the topsoil. P is applied to the paddy as fertilizer, and As and Zn are possible impurities in the fertilizers. The importance of the mobility data of the elements in the environmental studies is also discussed.
