Effects Of Organic Materials Incorporation On Dissolution And The Vertical Migration Of Cadmium In Paddy Soil

To inverstigate the effects of organic materials on dissolution and vertical migration of cadmium(Cd) in Cd-contaminated paddy soils under flooding condition, this study choosed 2 types of exogenous Cd polluted paddy soils(alluvial sandy paddy soil and yellow clayer soil) from Hunan Provencel and milk vetch and rice straw as test materials. By the methods of indoor cultivation test and soil column simulation experient, it was studied to illustrate the effects of the application of organic materials on the content of forms of Cd, total Cd and exchangeable Cd in Cd-contaminated soil, and to discuss influencing factors through the correlation anaiysis of dissolved organic carbon (DOC) content and pH value.It was aimed to provide scientific basis for the safe application of organic materials. The main results were as below:(1) Indoor flooded cultivation experiments results showed that:under the flooding condition of 60 days, Cd dissolution in Cd-contaminated soil was different form the kind and amount of organic materials, the time of cultivation and the type of soil. Comparison and adding 4% rice straw ash, the dissolution of Cd was smaller and little change in soil. It had a great influence to dissolve Cd in treatment of single fertilization of milk vetch and rice straw (the amount of 1% and 2%) and both with application in foster the prophase (1-5 d), and increased with increasing dosage, and the impact was smaller in late (30～60 d); in accordance with the relevant water Cd quality standard (10 μg·L-1) evaluation, the content of soil solution Cd was exceeded to 1.5-9.1 times in the early stage, closed to safety value in the late; According to the average dissolution rate of Cd, milk vetch and rice straw with fertilizer (1.89%)> rice straw applied alone (1.67%)> milk vetch single application (1.15%), alluvial sandy paddy soil (1.34%)> yellow clayer soil (1.26%).The correlation analysis of 1-30 d showed that the content of water soluble Cd was positively correlated with exchangeable Cd and DOC content, and was negative correlated with pH value during 1-30 days.(2) The results of indoor flooding soil column incubation experiment showed that: Under the saturated water culture condition of 0-60 cm heterogeneous soil, the vertical migration of Cd in 0-40 cm topsoil was related to the kinds and amount of organic material, training time and soil condition. The leakage solution of soil column bottom of all treatments were not checked out the water soluble Cd. Compared with contrast, at the early stage of the test (1-10 d) Cd of each treatment did not migrate in surface soil. At the test late (30-60 d), Cd could be migrated to 20 cm in yellow clayer topsoil, while Cd were about 30 cm in alluvial sandy paddy soil. Overall, the effects of milk vetch on the vertical migration of topsoil Cd was larger than rice straw. In the 60 d, compared with contrast, the average growth in total Cd of 2% milk vetch and 1% rice straw treatment were 23.3% and 14.6%. The growth of total Cd in soil, which was 154.7%, was the largest in the alluvial sandy paddy soil (20 cm) under the rice straw processing. Adding milk vetch and rice straw, the content of exchangeable Cd was increased in soil. The correlation analysis showed that the exchangeable Cd content in the soil column of each soil layer was positively correlated with the content of DOC.