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 were 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) were 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 promise as a means of decreasing tuber Cd uptake. Sulfate ions presumably promote increased soil adsorption of soil and/or fertilizer Cd compared with chloride ions, and so decrease Cd availability. We attributed the lack of difference in tuber and petiole Cd between K sources at two sites to either leaching, chloride in irrigation water, or at one site to a higher than desired rate of NPK fertilizer with the sulfate treatment. Any one of these may have offset decreases in Cd uptake due to the presence of sulfate ions.