FIELD STUDIES OF CADMIUM IN POTATOES (SOLANUM-TUBEROSUM L) .3. RESPONSE OF CV RUSSET-BURBANK TO SOURCES OF BANDED POTASSIUM

Six field experiments were conducted where Russet Burbank potatoes wer e grown with banded fertilizer consisting of diammonium phosphate (DAP ) and either potassium sulfate (K2SO4) or potassium chloride (KC1). At each site, rates of nitrogen (N), phosphorus (P) and potassium (K) we re matched as closely as possible for each K fertilizer treatment. At four of the six sites, potatoes grown with K2SO4 had tuber and petiole cadmium (Cd) concentrations 20-30% lower than did potatoes grown with KC1. The use of K2SO4 instead of KC1 appears to offer considerable pr omise as a means of decreasing tuber Cd uptake. Sulfate ions presumabl y promote increased soil adsorption of soil and/or fertilizer Cd compa red with chloride ions, and so decrease Cd availability. We attributed the lack of difference in tuber and petiole Cd between K sources at t wo sites to either leaching, chloride in irrigation water, or at one s ite to a higher than desired rate of NPK fertilizer with the sulfate t reatment. Any one of these may have offset decreases in Cd uptake due to the presence of sulfate ions.