[Bioavailability of exotic zinc and cadmium in purple soil]

Correlation analysis between seven forms and available amounts (extracted by DTPA) of Zn and Cd, and their path analysis from soil to lettuce (Lactuca sativ L.) were conducted to evaluate bioavailability of zinc and cadmium and their contributions to the plant. The results showed that exchangeable Zn and Cd were significantly correlated to available Zn and Cd (r = 0.954 and 0.953) at significance level of 0.01, and path coefficients of exotic Zn and Cd to tissue Zn and Cd were 1.267 and 1.168 respectively, indicating the high bioavailability of exchangeable Zn and Cd in purple soil. Exotic Zn and Cd made the most contribution to the plant, while the path chain coefficients of CAB-Zn, MnO-Zn, and Cd to the plant by indirect action of exchangeable forms were 0.856, 0.592, 0.723, respectively, showing that they may make some other contributions to tissue Zn and Cd through exchangeable forms. Therefore, exchangeable Zn and Cd are not only highest available, but also are bioavailable bridges and main paths from purple soil to the plant.