Method for assessing plant-available cadmium in soils

The suitability of several extractants was tested for assessing the plant-available cadmium (Cd) in a few selected soils of South Australia. The amount of Cd extracted by 7 extractants (0.01 and 0.05 M CaCl(2), Na(2)EDTA, DTPA-TEA, M NH(4)NO(3), AAAC-EDTA, and M NH(4)Cl) was related to the Cd concentration in the stem and leaves of durum wheat (Triticum aestivum L. var. Excalibur) grown in the greenhouse for 5 weeks. Soil extraction with M NH(4)Cl gave the best overall prediction of extractable Cd with plant Cd concentration (r = 0.928, P < 0.001) compared with the other extractants. Multivariate models were derived to predict both the total and plant-available Cd from the soil factors. The aqua-regia-extractable Cd was on an average 45.3% of the total Cd content, as determined by HF-HClO(4) digestion, and at best could represent the easily extractable fraction of soil Cd. Around 77% of the variation in total Cd content of the soils could be explained using selected soil properties, such as free Fe, organic C, and pH. The accumulation of Cd by wheat plants from the soils studied could be assessed using the multivariate model, log leaf Cd = -0.2107 + 1.2281 log Cd NH(4)Cl, with high correlation (R(2) = 0.93). The coefficient of determination could be improved further (R(2) = 0.99) with the inclusion of the soil variables free Fe, pH, organic C, and clay contents: log leaf Cd = 0.2095 + 1.2556 log Cd NH(4)Cl + 0.0219 Fe + 0.0149 clay - 0.2633 org. C - 0.0577 pH.