| Cadmium (Cd) is one of the most toxic and serious environment polluting heavy metals. The application of amendments is an important approach to remediate Cd contaminated soils. With the rapid economic development, the heavy metal pollution is fairly conspicuous in the Pearl River Delta region.Aiming the soil type of Pearl River Delta region, pot experiments were conducted to campare the effects of 4 amendments [lime, calcium-magnesium phosphate (Ca-Mg-P fertilizer), alkali slag and peat] on inhibited Cd uptake of Brassica Chinesis in soils which by adding 3 level of Cd solution(0, 1, 5 mg·kg-1). Then pot experiments were conducted to determine the amount of amendments which were screened in the Cd contaminated vegetable soil and soil culture experiments were conducted to examine mechanisms of amendments from the changes of Cd speciations. At last, the effect of amendments and their dosage were tested through a field trial. This thesis systematically studied the amendments and dosage for remediating large areas of Cd contaminated vegetable fields. The results were as follow:In this research, applications of lime, Ca-Mg-P fertilizer and peat did not inhibit the growth of Brassica chinesis, but the high dosage of alkali slag (15 g·kg-1) was inhibited and low dosage of alkali slag (3 g·kg-1) promoted the growth of B. chinesis.Adding 1,5 mg·kg-1 Cd solution did not significantly inhibited the growth of B. chinesis, but 1 mg·kg-1 Cd inhance and 5 mg·kg-1 Cd decrease the biomass of B. chinesis and there was a significantly positive correlation between the Cd concentration of Brassica chinesis and the adding Cd (r = 0.847, p< 0.01).Compared with the control treatment, application 4 amendments remarkably decrease shoot Cd content in B. chinensis in in soils of adding Cd pollution. The order of efficiency of the 4 amendments on reducing shoot Cd content is lime≈peat> alkali slag> Ca-Mg-P fertilizer. The effect amendments were consistent in soils of adding diferent Cd pollution.Lime and peat still inhibited the Cd uptake of B. chinesis in the Cd contaminated vegetable soil and and there was a positive correlation ( r =-0.668,-0.785,p < 0.05) between the inhibitory effect and the application dosage. However, different dosage of alkali slag which reduced the dosage campare with the first experimet showed no obvious effects on shoot Cd concentration, but significantly increased root Cd concentration of B. chinensis.The major mechanism of the amendments which remediate Cd contaminated soil is the change of the Cd speciation. A modified BCR three-step sequential extraction procedure was used to determine Cd speciation in the Cd contaminated soil. Lime and peat reduced the exchangeable, acid-and water soluble Cd and increased the residual Cd. Besides peat could increase the oxidisable Cd. Amendments all improved soil pH, but they have different effects on the DTPA-Cd. Lime greatly decreased DTPA-Cd but peat have trend to increase DTPA-Cd.This may be due to DTPA extraction consist of exchangeable, acid-and water soluble Cd. Field test result is consistent with the results of pot experiment. Among three amendments, the peat is showed to be the best one for decreasing the shoot Cd, and the optimum dose is 20 g·kg-1. Second one is lime. Alkali slag is not suitable to be used as an amendment to remediate Cd contaminated soil. Comparison between the two crops indicates that amendments still decreased Cd concentration in B. chinensis in the second crop in the pot experiment and filed test. However, the effect of inhibition decrease. So, application the amendment appropriatly to increase its effect at the second crop.
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