Effect Of Phosphates On Adsorption And Bioavailability Of Cadmium In Calcareous Soils

This paper studied the P-Cd interaction in the calcareous soil, and its effects on Cd availability, plant growth and the Cd accumulation in plants through the methods of absorption-desorption experiment,indoor soil cultivation and pot trial. The main results were as follows: 1. In the tested calcareous soil,after adsorbed different amounts P , i.e. 8.73, 450, 825, 1325, 2612 mg kg-1, respectively, the amounts of Cd secondary sorption increased with the amounts of P adsorption increased in the soil, especially when the absorption amount of P exceed to 825 mg kg-1, the Cd absorption amount increased more significantly. The isotherms of Cd secondary adsorption with different amount of P adsorbed indicated that increased P amount in calcareous cinnamon soil could increase the adsorbing capacity of Cd2+. 2. After adsorbed different amount Cd, i.e. 44.99, 123.23, 190.60, 352.68, 839.33, 1217.79, 1460.61 mg kg-1, respectively, the amounts of P secondary sorption increased with the amounts of Cd adsorption increased in the soil. The amount of Cd desorption (0.1 mol L-1KNO3) increased with the amounts of Cd adsorption increased. When the absorption amount of Cd less than 825 mg kg-1, the proportion of the amounts of KNO3 desorbed Cd to the total desorbed amounts was significantly increased, and the proportion increased with the P concentration increased. But when the absorption amount of Cd more than 825 mg kg-1, the proportion was significantly decreased, and the proportion decreased with the P concentration increased. 3. After added certain amount of P and Cd to the tested soils and incubated for 90 days, the available P content in the soil was significantly decreased with the Cd concentration increased; and the content of DTPA extractable Cd was significantly increased with P concentration increased. 4. The pot trial with different forms or amount of P and Cd application showed that the biomass of tobacco decreased obviously with the increased of the Cd applied, but when P concentration increased in the soil could alleviate this trend of decrease, and the biomass increased significantly with the increased of the P applied. All of the forms P treatments could increased the plant biomass, and the treatments of KH2PO4, DCP, Al-P and Fe-P which have high bioavailability could significantly increase the biomass of tobacco than that of other P forms treatments. 5. The Cd content in the plant decreased with the increased of the amount of P applied, but increased significantly with the increased of Cd in the environment. Added Cd into the soils could decreased the P content in the plant, and the Cd could restrain the transfer of P from the roots to the leaves. The P content in the plant decreased significantly with the increased of the amount of Cd applied under different forms P treatments, and the Cd concentration effects on the phosphorus accumulation was higher than that of P forms treatments.