Evaluation of extraction methods for plant-available soil cadmium to wheat [Triticum aestivum] by several extraction methods in cadmium-polluted paddy field

To develop a new method for the extraction of plant-available cadmium (Cd), the correlation between the Cd content of polluted soil extracted with several extractants and the Cd content of wheat plants (variety "A";Triticum aestivum L.) was examined. Among the HCl concentrations of soil extractants tested, the content of 0.025 mol L(-l) HCl (HCl 0.025)-extractable Cd of soil showed a significant correlation with the Cd content of wheat grain and Cd uptake by shoot. The correlation between the soil Cd content extracted with 1 mol L(-l) NH4Cl and the Cd content of wheat grain was nearly the same as that in the case of HCl 0.025. In contrast, other reagents such as MgCl 2, diethylenetriaminepentaacetate (DTPA) and tetra-sodium pyrophosphate (Na4P2O7) could not give a good correlation between the extractable Cd content of soil and the Cd content of wheat grain. Therefore, it was considered that HCl 0.025-extractable Cd is a suitable indicator of the content of plant-available Cd of soil to wheat. This extraction method can be applied to weakly acid grey lowland soil. Using the equation for the relation between the content of HCl 0.025-extractable Cd of soil and the Cd content of grain of the wheat variety "A", the Cd content of grain of other 11 wheat varieties was evaluated. The wheat variety "A" showed the lowest absorption of Cd. The Cd content of variety "B" grain was located on the regression line of that of variety "A", suggesting that both varieties exhibited the lowest ability to absorb Cd among the varieties tested. Grain yields of both "A" and "B" vatieties were reasonably high. On the other hand, other varieties showed a substantially high ability to absorb soil Cd compared with the varieties "A" and "B". The new method proposed for the determination of the content of plant-available Cd proved to be suitable for the evaluation of plant-available Cd of soil and also for the screening of wheat varieties with a high or low Cd accumulation capacity in grain.