PARTITIONING AND DISTRIBUTION OF CADMIUM AND ZINC IN SELECTED CULTIVATED SOILS IN NORWAY

Eleven samples, collected from three Norwegian cultivated soils under different management practices, were analyzed by sequential extraction to isolate five operationally defined fractions of Cd and Zn. On average, 47, 4, 33, and 5% of the sum of the Cd fractions (SIGMACd) were found as weakly adsorbed (F1), adsorbed (F2), strongly adsorbed (F3), and very strongly adsorbed (F4) forms of the element, respectively. Eleven percent was regarded as incorporated in resistant minerals (F5). The relatively high proportion of the F1 fraction indicates that much of the Cd under these conditions, may be easily available to plants. In contrast to Cd, the highest percentages of SIGMAZn (31 and 47%), on average, were associated with strongly (F3) and incorporated with resistant minerals (F5), respectively. The F2 and F4 fractions contributed little to the sum of the fractions for both elements, and the low percentage of the weakly adsorbed (F1) for Zn is indicative of low mobility and availability of the element in these soils. For Cd, F1-F3 were directly correlated with OC and TFe. OC also seemed to be important in retaining F4, whereas F5 correlated best with clay. Positive correlations were also found between Fl and F3 of Zn with OC. The direct relation between F3 and TMn may indicate a stronger association of Zn with the oxides of Mn than of Fe in these soils. F5 of Zn correlated best with OC, TFe, and silt.