Effects of liming on uptake of lead and cadmium by Raphanus sativa

Although liming soil to reduce the heavy metal uptake by plants has been recommended generally, there is some disagreement with the practice based on the results of recent studies. Radishes, Raphanus sativa L. var. Paekyong, were grown in greenhouse pots which were filled with soils treated with 1.52 mg kg(-1) Cd and 25.37 mg kg(-1) Pb, respectively and amended with lime at five rates of 0, 0.25, 0.5, 1.0, and 2.0% by dry soil weight. Plants were harvested three times at 25, 50, and 75 days after sowing and the roots and shoots separated. After the plant samples were digested with HNO3-HClO4, Cd was analyzed by flame AAS and Pb by graphite furnace AAS. A large amount of Cd was translocated into the radishes, which accumulated dramatically with time. Compared to Cd, Pb uptake was very low and accumulated slowly. Cd contents were very much higher in the shoots than the roots, but Pb was not significantly different. Liming or increased soil pH decreased Cd uptake markedly with increased lime level; Pb influence was negligible. Yields were decreased with excessive liming, but not by the levels of Cd or Pb added.