EFFECT OF POTASSIC AND PHOSPHATIC FERTILIZER TYPE, FERTILIZER CD CONCENTRATION AND ZINC RATE ON CADMIUM UPTAKE BY POTATOES

In some areas of southern Australia, cadmium (Cd) concentrations in ex cess of the Australian maximum permitted concentration (0.05 mg kg(-1) fresh weight) have been found in tubers of commercially grown potato (Solanum tuberosum L.) crops. Field experiments were therefore conduct ed in various regions of Australia to determine if Cd uptake by potato es could be minimised by changes in either phosphorus (P), potassium ( K) or zinc (Zn) fertilizer management. Changing the chemical form in w hich either P fertilizer (monoammonium phosphate, diammonium phosphate , single superphosphate and reactive rock phosphate) or K fertilizer ( potassium chloride and potassium sulfate) were added to crops had litt le influence on tuber Cd concentrations. Fertilizer Cd concentrations also had little influence on tuber Cd concentrations, suggesting that residual Cd in the soil was a major contributor to Cd uptake by the cr ops on these soils. Addition of Zn at planting (up to 100 kg Zn ha(-1) ) significantly reduced tuber Cd concentrations at four of the five si tes studied. However, the largest variation was between sites rather t han between treatments, with site mean tuber Cd concentrations varying tenfold (from 0.018 to 0.177 mg Cd kg(-1) fresh weight). Factors asso ciated with irrigation water quality at the sites, in particular the c hloride concentration, appeared to dominate any effects of changing fe rtilizer type or Cd concentration.