EFFECTS OF SULFATE ON CADMIUM UPTAKE BY SWISS-CHARD - II - EFFECTS DUE TO SULFATE ADDITION TO SOIL

Sulfate complexation of Cd in nutrient solution has been shown to have little impact on Cd uptake by plants. This study examined the effect of sulfate added to soil on Cd concentrations in soil solution and Cd uptake by Swiss chard (Beta vulgaris L. cv. Fordhook Giant). Swiss cha rd was grown in soil which was wetted with complete nutrient solution containing equivalent salt concentrations of NaNO3 or Na2SO4. Plant gr owth was reduced by increasing both NO3 and SO4 concentrations in soil solution, with growth reductions similar for both salts. The Cd conce ntration in soil solution increased (P < 0.05) more consistently with increasing concentrations of SO4 compared to NO3 in soil solution. Sol ution speciation, calculated with GEOCHEM-PC, showed significant incre ases of Cd2+ activities with increasing salt rates. Shoot Cd content i n 19-day-old Swiss chard plants was marginally but significantly (P < 0.05) increased with increasing SO4 concentration but no effect was ob served with increasing NO3 concentration. These results are compared w ith earlier work on the marked effect of Cl- salinity on Cd availabili ty in Swiss chard. Possible mechanisms explaining the smaller effect o f SO4 compared to Cl on Cd availability are proposed.