SPECIATION OF CADMIUM IN SOIL SOLUTIONS OF SALINE SODIC SOILS AND RELATIONSHIP WITH CADMIUM CONCENTRATIONS IN POTATO-TUBERS (SOLANUM-TUBEROSUM L)/

Fifty commercial potato crops and associated soils were sampled. Soil solutions were extracted from rewetted soils by centrifugation, and so lution composition was related to Cd concentrations in tubers. Soils w ere also extracted with 0.01M Ca(NO3)(2) and 0.01M CaCl2 solutions, an d Cd2+ activities in the extracts were calculated by difference using the stability constants for formation of CdCln2-n species. The soils h ad saline solutions (>4 dS/m), and Cl- and SO42- in solution markedly affected the speciation of Cd in soil solution, with chloro-complexes, in particular, dominating. While low soil pH was associated with high (>25 nM) concentrations of Cd in soil solution, chloro-complexation a lso led to high concentrations of Cd in solution, even at neutral to a lkaline soil pH values. Tuber Cd concentrations were not related to ac tivities of Cd2+ in soil solution or to activities in dilute salt extr acts of soil. Tuber Cd concentrations were related to the degree of ch loro-complexation of Cd in solution. The relationship of tuber Cd conc entrations to chloro-complexation in soil solution suggests that Cd sp ecies other than the free Cd2+ ion are involved in the transport throu gh soil and uptake of Cd by plants.