Prediction of cadmium concentrations in potato tubers (Solanum tuberosum L.) by pre-plant soil and irrigation water analyses

Potato tubers can accumulate high concentrations of cadmium (Cd) in edible portions, so that techniques to determine high risk Cd environments are req uired by growers. The use of combined soil and irrigation water analyses pr ior to crop planting was investigated as a means to predict risks of Cd acc umulation in tubers. Soils and irrigation waters were analysed at 134 sites in the major potato production areas in Western Australia, South Australia , Tasmania, Victoria, and New South Wales. Irrigation waters were analysed for electrical conductivity (EC), major cations, and anions. Cadmium was ex tracted from soil using aqua regia (1 : 3 HNO3 : HCl), EDTA (ethylenediamin e-N,N,N',N'-tetraacetate), DTPA (diethylene-triamine-pentaacetate), 0.01 M CaCl2, 0.01 M Ca(NO3)(2), 0.1 M CaCl2, and 1.0 M NH4NO3. The preferred test procedure was validated in a subsequent sampling and analysis program at 3 9 sites. Irrigation water quality (EC or Cl concentration), measured prior to planti ng, explained the greatest variation in tuber Cd concentrations. Of the soi l test procedures, only Cd extracted by 0.01 M CaCl2 significantly improved the predictive capacity of water EC. These 2 measures explained >55% of th e variance in tuber Cd concentrations. The data set were transformed to gen erate a probability curve for exceeding Cd concentrations of either 0.05 or 0.1 mg/kg fresh weight, the latter being the current maximum permitted con centration (MPC) in Australia for potato tubers. The probability of producing potato tubers exceeding 0.05 and 0.1 mg/kg fre sh weight was >50% once irrigation water EC increased above 1.4 and 3.0 dS/ m, respectively. Using the relationships developed, growers should be able to quantify Cd risks by a simple test of irrigation water EC prior to plant ing and, if further precision is needed, also determine CaCl2-extractable C d in soil.