Guizhou Cadmium Yellow Soil In The Biological Effectiveness Of Regulation And Its Mechanism

Choose yellow soil which is typical in Guizhou privince to be trying soil. Comprehensive methods including pot experiment and laboratory culture experiment were adopted in this study, we comprehensively and systematically compared the effects of some typical inhibitors and their different combined ways in inhibiting Cd bioavailability in yellow soil, further studied the laws and affecting factors of Cd's transfer and transformation in soil-plant system, revealed the mechanisms inhibitors function, and explored the practicable inhibitor prescriptions and their usage. The results are expected to provide reliable techniques for controlling Cd pollution of agricultural soils in Guizhou and it is also significant to ameliorate soils polluted by other kinds of heavy metals.The tested inhibitors are listed as follows: distiller's grain, pig manure, oil meal, coal ash, ZnSO₄ and lime. Pot experiment, in which cabbage was chosen as the tested plant, involved 12 treatments, 3 replications each. Biomass and Cd concentration indifferent parts of plants was observed to study the effects of different treatments. Laboratory culture experiment with the same treatments as pot experiment but 2 replications each. To study the influence of inhibitors on the dynamic process of transformation and variation of availability of Cd in soil, laboratory cultured soil was sampled in certain interval during the 90-day cultured period for the analysis of Cd availability and speciation. The main conclusions are as follows:1. Using inhibitor could enable pH of soil to have the varying degree rise, especially for distiller's grain. Next is pig manure; using the different amount of the lime, In the 15 days ago, their pH is much higher than the control, which is 1.2%CaCO₃>0.8%CaCO₃>0. 4%CaCO₃>0. 2%CaCO₃. After 15 days, only pH of 0.4% lime is higher than control 2. Other does of lime is lower than control 2.2. Using inhibitor could significantly affect cabbage biomass. The ratio of the maximum of biomass (treated by distiller' s grain) to the minimum (treated by ZnSO₄) was 38. 88. It showed that the biomass would dramatically increase when added distiller' s grain,pig manure,0. 8%CaCO₃,1.2%CaCO₃, especially added distiller' s grain only. The range of this increase was 96. 82%—381. 14%. The biomass would decrease when added ZnSO₄.3. The tested inhibitor had inhibitions on plant' s uptake for Cd with different degree. Among these inhibitors, distiller' s grain that caused Cd concentration to decrease by 57. 06% compared to the control had an optimum inhibition effect. ZnSO₄was the worst one, dropped 0.969%. The magnitude sequence of inhibition effects among three kind of organic matters is distiller' s grain>pig manure>oil meal. Coal ash is not very obvious effect. Lime application rate of 0. 8% had an optimum inhibition effect. Consideration of the inhibitions on plant' s uptake for Cd and the impact on cabbage growth, adding 0.8% lime is more reasonable.4. In the yellow soil, the proportion of each form is: Exch-Cd(63. 43%)> Res-Cd (24. 30%) > BO-Cd (3. 09%) > CARB-Cd (2. 69%) > Te,MnO_x-Cd (2. 31%). The effects of different inhibitors on cadmium' s fraction distribution and availability were different. All inhibitors reduced Exch-Cd by 4.11%—35. 87%; And increased Res-Cd by 2. 47%-84. 16%. Making Cd transform to unavailable state or slowly available state is the chemical essence of inhibitors to restrain the bioavailability of Cd. Other fraction of Cd occupied a small proportion, but all reflected the direct of fraction transformation; All inhibitors reduced Avail-Cd by 2. 78%-29. 97%. Each form of Cd went to stable after two months.5. In this test, Te.. MnO_x-Cd had the maximum effect on plant' s uptake for Cd. The linear correlation coefficient between Cd concentration of parts of the ground and Te> MnO_x-Cd is respectively 0. 771; All the cadmium have negetive correlation with plant's uptake, except Exch-Cd. The linear correlation coefficient between Cd concentration of parts of the ground and underground for Avail-Cd is respectively 0.699 and 0.870.