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 excess 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 conducted in various regions of Australia to determine if Cd uptake by potatoes could be minimised by changes in either phosphorus (P), potassium (K) or zinc (Zn) fertilizer management. Changing the chemical form in which 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 little 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 crops 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 sites studied. However, the largest variation was between sites rather than between treatments, with site mean tuber Cd concentrations varying tenfold (from 0.018 to 0.177 mg Cd kg(-1) fresh weight). Factors associated with irrigation water quality at the sites, in particular the chloride concentration, appeared to dominate any effects of changing fertilizer type or Cd concentration.