Remediation Of Acidic Soil With Cd Contaminated By Combined Application Of Lime And Organic Matters With Its Bio-effect

China is the largest producer and consumer of rice in the world,more than 60%of Chinese people take rice as the staple food,even higher proportion in southern China.Rice is the bulk cereal commodity,under the great pressure of surface source pollution of heavy metals in farmland,rice is facing severe risk of Cd contamination because of its strong storage capacity of Cd.In lately years,such incidents,rice with Cd-contaminated occurred frequently in China,hence more and more resident pay attention into concern of food security,and the remediation of soil pollution in agricultural land has become a research hotspot.In order to achieve goal of ensuring food,vegetables and water quality safety furthermore providing basic guarantee of whole society,finally safeguarding human health,promoting the work of soil pollution control,farmland restoration,and improve soil quality of field,then ensuring food quality and safety of agricultural products,such above work,under a new situation,are necessary for the ecological defense,but also promoting social harmony and stability even national economic development.Therefore,this study,in order to research the effect on fractions change of Cd in soil,absorption and distribution of Cd in rice plants by combined application of lime and organic matters,as the mean time exploring the mechanism of fractions change of Cd in soil,response of soil bacteria to physical and chemical factors,in-situ experiments were conducted on indoor and paddy field with Cd-contaminated soil in Chongqing.Also bio-effects brought by the application of the remediation agent were studied,thus the remediation program was optimized by combining the indoor and outdoor remediation effects,the treatment of each remediation agent has a certain reference significance for the local realization of the safe utilization of agricultural contaminated soil and the safe output of food.The conclusions were as follows:(1)In the experiment of lime dosage,value changed of pH was mainly determined by the dosage of lime in acidic soil,and the linear correlation were showed 0.77～0.93.But these curves of fitting equation(R~2>0.99)showed,that pH value and lime dosage were not linear correlation completely,it meant with a higher soil pH value,ability of raised pH value became down by the same lime dosage.(2)In the study,soil pH value,OM contents and CEC were enhanced with application of remediation agents,therefore,fraction of Cd was transformed from acid extractable fraction to oxidizable,reducible and residual fractions,thus reducing its activity.(3)In the soil incubation experiment,activity of Cd in soil was reduced significantly with the increase of OM contents and CEC in experimental group of purple soil.In experimental group of yellow soil,however,OM contents showed more effective than pH and CEC on passivation of Cd.Overall,the effect on passivation of Cd,application of lime combined with organic materials on soil were better than lime application solely.And in two types experimental soils with Cd-contaminated,treatment of lime combined with oil cake reached the best effect of remediation,which result showed that maximum decrease of effective Cd content(64.91%).(4)In the field plot experiment,it fund that activity of Cd was inhabited effectively with application of remediation agents,thus reducing accumulation of Cd in rice plants and grains.Among these treatments,application of lime combined with oil cake was the best measure as it showed the reduction of acidic extractable Cd(31.25%),Cd in rice plants(33.32%),and the lowest contents of Cd in polished rice which was reduced 42.17%compared with CK.The result also showed that Cd contents in brown rice which treated by remediation agents were higher than Chinese limit standard(GB 2762-2017),but Cd contents in polished rice which highly processed were lower than Chinese standard after treatment.In order to ensure human health,findings suggesting local residents should reduce the consumption of brown rice.(5)Findings showed that application of remediation agents effectively improved the biomass of rice,and treatment of lime combined with biochar got the best effect on the enhance of wet weight of straw,and treatment of lime combined with humic acid fertilizer showed the best effect on the enhance 100-grains weight of rice.(6)Correlation analysis showed that the number of bacterial communities in purple soil and yellow soils were positively correlated with the activity of Cd,and the Cd stress level set in experiment posted a stimulating effect on the growth of soil bacteria.But,after applied of remediation agents,the bacterial growth curves of each treatment tended to converge and showed a consistent trend.