Remediation Of Cd Contaminated Brown Red Soil-pakchoi System By Compost

The remediating effect of compost on the cadmium-contaminated plant-soil system was evaluated and the mechanism was discussed, through pot experiment of pakchoi. The soil was sampled from Huazhong Agriculture University, Wuhan city, and was treated with various levels of cadmium (0, 2, 10, 50 mg kg^-) and increasing amounts of compost (0, 30, 60, 120 g kg^-1). The main results were listed as following:1. Compost application improved the performance of pakchoi in the Cd-contaminated soil. In the soil treated with 2 mg kg^-1 Cd, the pakchoi yield, chlorophyll and vitamin C content after compost application achieved the level of control without Cd pollution.2. Compost application inhibited the transfer ability and decreased the Cd uptake of pakchoi. Absorption coefficient was decreased by more than 62.6%, and the Cd uptake more than 56.2%. In general, the decrease of pakchio performance was more pronounced in higher Cd contaminated soil.3. Compost applied amount (X₁), soil Cd concentration (X₂) and the plant responses (F_p) accorded with the following equation:The compost amount could be calculated to achieve the best performance of pakchoi at various soil Cd level.4. Compost application enhanced the microbial biomass carbon content in the Cd-contaminated soil, promoted the microorganism growth. The microbial biomass carbon content after compost application at 2 mg kg^-1 Cd treatment exceeded the level of control without Cd pollution. Soil microbial biomass carbon (F_m), compost applied amount (X₁) and soil Cd concentration (X₂) complied with the following relation, which can work out the appropriate amount of compost application to achieve the largest soil microbial biomass carbon:5. Compost application increased the ratio of bacteria/fungi and bacteria/actinomycetes, consequently changed microbial community in the Cd-contaminated soil.6. Compost application increased the activity of sucrase, urease, phosphatase and proteinase, improved the soil biochemistry property. In the soil treated with 2 mg kg^-1 Cd, the activity of sucrase, urease, phosphatase after compost application achieved or exceeded the level of control without Cd pollution. Soil enzyme activity response (F_e), compost amount (X₁) and Cd concentration (X₂) acted in accordance with the following equation:The compost amount could be calculated to achieve the best performance of soil enzyme activity at various soil Cd levels.7. Compost application transformed the soil soluble & exchangeable Cd mainly to soil organic-bound. Soluble & exchangeable Cd concentration was decreased by 47.8% - 69.8%, and organic-bound fraction was increased by 1.8 - 13.3 times in comparison with unmended soil. The percentage of Cd form in the Cd-contaminated soil without compost was following: soluble & exchangeable > inorganic-bound > residual, organic-bound; after compost application: organic-bound, inorganic-bound > soluble & exchangeable, residual. Therefore, compost application decreased the bioavailability of soil Cd. Pathway analyses showed that compost redistributed soil Cd mainly by enhancing the soil organic matter and soil microbial biomass.The results suggested that compost application was very effective in the restoration of Cd-contaminated soils. However, the field experiment was required before practicing because of the complexity of soil heavy metal pollution and the diversity of influence factor in the nature.