The Effects Of Different Passivants Combinations On Cadmium Bioavailability In Paddy Soils

The study selecting Qingxi Town,Zhenyuan country as research areas,the effects of different combinations of passivating agents on soil physical and chemical properties,Cd bioavailability,uptake and accumulation of Cd and yield in rice were studied viarice field and pot planting experiments to provide a scientific reference for remediation of heavy metals in paddy soils from Guizhou province.The results of the study are as follows:?1?The pH and CEC in soil were effectively improved with combinations of different passivating agents,and the contents of organic matter in soil were effectively improved via applying organic fertilizer.In field experiment,the effects of different passivating agents combinations on physical and chemical properties of the three varieties of rices were the same.The teratment quicklime+passivating agent 4obviously improved the pH in soils of Zhongzheyou 1,Yixiangyou 2115,Yuxiang 203,and the pH values in creased by 0.65,0.81 and 0.73 pH units respectively.The organic matter enhanced respectively 3.43g/Kg,4.58g/Kg and 3.05g/Kg with the treatments of quicklime+organic fertilizer,quicklime+organic fertilizer,and organic fertilizer.The CEC enhanced respectively 5.16cmol/Kg,5.24cmol/Kg and4.67cmol/Kg with the treatments of quicklime+passivating agent 4,quicklime+passivating agent 4 and quicklime+passivating agent 3.The changes of physical and chemical properties of soil and Rhizosphere Soil in the three kinds of rice were the same.In non rhizosphere soil,the whole pH was higher than the rhizosphere soil,and the CEC in the non rhizosphere soil was lower than the rhizosphere soil,but the organic matter was not significantly changed.In the pot experiment,the maximum increase of pH,organic matter and CEC in soil are the lime+passivating agent 4+organic fertilizer,lime+passivating agent 3+organic fertilizer and lime+passivating agent 2+organic fertilizer,which are up 1.04 pH units,8.55cmol/kg and6.92g/kg respectively.?2?The combination of different passivating agents can effectively reduce Cd exchangeable content in soil.In the field experiments,the highest reduction of Cd exchangeable ratio in the paddy soils of Zhongzheyou 1,Yixiangyou 2115 and YuXiang 203 was 4,lime+passivating agent 1 and lime+passivating agent 3,respectively,which decreased 14%,16.4%and 16.1%respectively,and the non rhizosphere soil Cd in the paddy fields of three rice varieties could be exchanged.The whole change content is lower than the rhizosphere soil as a whole.In pot experiment,the highest decrease rate of Cd exchangeable proportion of soil was quicklime+passivating agent 2+organic fertilizer,which decreased by 8.5%.?3?The combination of different passivating agents can effectively reduce the concentration coefficient BCF of rice root to Cd,the transport coefficient TF_rss of root to straw and the transport coefficient TF_hbb of rice husk to brown rice,and the influence of Cd straw to rice hull transport coefficient TF_shh is unstable.The transport coefficients of all three rice varieties were ranked as follows:TF_hb>TF_sh>TF_rs.The enrichment coefficient of Cd in rice root Cd of zhe you no.,Yixiang you 2115 and Yu Xiang 203 was the best treatment for BCF reduction,which were lime+passivating agent 4?2.37?,lime+passivating agent 1?2.50?and L+D4?1.96?.The maximum reduction of the transfer coefficient of root to straw was the quicklime+passivating agent 3?0.17?.With quicklime+passivating agent 4?0.18?and quicklime+passivating agent 4?0.12?,the maximum reduction of the transfer coefficient TF_shh of straw to rice husk is lime+organic fertilizer?0.44?,lime+passivating agent 4?0.49?and lime+passivating agent 4?0.32?,and the transport coefficient of rice hull to brown rice is most reduced by TF_hb.The major treatments are quicklime+passivating agent 3?0.93?,quicklime+passivating agent 2?0.75?,quicklime+passivation agent2?0.59?.?4?The combination of different passivating agents can effectively reduced the accumulation of Cd in different parts of rice.Compared with CK treatment,the content of Cd in rice root,straw,rice husk and brown rice in other treatments decreased 6.6%⁴5.6%,14.1%⁵0.5%,26.9%⁵9.7%and 13.0%⁶8.7%respectively.The Cd content of the lime+passivating agent 1+organic fertilizer,lime+passivating agent 2+organic fertilizer,lime+passivating agent 3+organic fertilizer and lime+passivating agent 4+organic fertilizer were less than 0.2mg/kg,which was in line with the national standard of food pollutants.?5?The combination of different passivating agents can effectively improved rice yield,and the effect of organic manure treatment is more obvious.In the field experiments,the best treatments for rice yield in the rice fields of Zhongzheyou 1,Yixiangyou 2115 and Yuxiang 203 were organic manure?8.6t/hm²?,lime+organic fertilizer?8.8t/hm²?and lime+organic fertilizer?7.0t/hm²?.In pot experiment,improve rice yield the best is lime passivation agent+1+organic fertilizer?42.5g/pot?.