Application Study On In-situ Remediation Of Safe Use Farmland Soil With Mild To Moderate Cd Contamination

Soil types and properties are quite different in China and the spatial soil distribution is"South acidic and north alkaline soil".The degree of soil contamination by Cadmium?Cd? in different regions is different,and the area of safe use farmland soil with mild and moderate is dominant.In-situ remediation is more suitable and economically feasible for Cd-contaminated soil remediation in large-scale application compared with other technologies.A success of in-situ immobilization remediation of Cd-contaminated soil depends on the low bioavailability of soil Cd and the soil ecological function.one to two year laboratory experiments or small-scale field experiments are not enough to support large-scale application of soil remediation.In this study,the safe use of mild to moderate-acidic Cd-contaminated paddy soils and mild alkaline Cd-contaminated wheat soil were remediated and fertilized,where biochar,sepiolite and fulvic acid-microbial agents were applied as the conditioning agents.The field plots and full-scale experiments were conducted for in-situ remediation and fertilization of Cd-contaminated farmland with multi-parameter evaluation and automatic modeling.Biochar and sepiolite were used as soil conditioners for the remediation of safe use weak-acidic Cd-contaminated paddy soil,and the reasonable dosage of 1.00% of biochar and sepiolite?0.50%+0.5%,w/w?was determined by field plot experiments.The reliability and stability of biochar and sepiolite for the remediation of mild Cd-contaminated paddy soil were evaluated with multiple parameters under 4-year full scale experiment with low-dose multiple application of the two agents.Biochar and sepiolite effectively inhibited the Cd uptake by rice and the highest rice yield was 9010kg/hm².Soil p H increased by 1.46,soil available Cd decreased by 22.42%,and the rice Cd reduced by 53.06%-88.03%,which fully met the requirement of the maximum limit value of 0.2 mg/kg of Cd in rice in National Food Safety Standard Limits of Pollutants in Food?GB 2762-1017?.Soil nutrients,organic matter,rhizosphere microorganisms and enzyme activities were enhanced with the application of biochar and sepiolite.The comprehensive analysis showed that 3-year continuous remediation was better than 1-year or 2-year continuous remediation.After biochar and sepiolite application was stopped,the remediation effectiveness remained stable in the following years.There were a negative correlation between soil available Cd,rice Cd and soil p H and a very significant positive correlation between rice Cd,hull Cd,straw Cd and root Cd?P<0.01?.And an extremely significant correlation between Cd in rice plant and environmental parameters?P<0.01?was observed.However,linear regression analysis shows that there was a multicollinearity relationship between these parameters.Principal component and stepwise regression analysis showed that there was a significant positive correlation between rice Cd and hull Cd and a significant positive correlation between hull Cd,soil available Cd and straw Cd jointly influenced hull Cd,and the accuracy of modelling reached 96.6%.The decrease of rice Cd could be attributed to the increase of soil p H,the decrease of soil available Cd and the inhibition of Cd transfer in rice plant with biochar and sepiolite.On the basis of remediation of safe use mild cadmium contaminated soil,field plot experiments for the remediation of moderate Cd-contaminated weak-acidic paddy soil were carried out with biochar and sepiolite.When biochar and sepiolite were 2.00% and 2.50% in field polt experiment,60.00% and 80.00%plots met to the requirement of the lowest rice Cd,and the lowest rice Cd was 0.041 and 0.098 mg/kg,respectively.There was a significant correlation between pairings of soil p H,soil available Cd and rice Cd?P<0.01?.The mechanisms of weak-acidic moderate Cd-contaminated paddy soil remediation was consistent with those of mild Cd-contaminated soil remediation.The fitting equation Y=1.227+0.792X₁-0.173X₂?R²=0.856,Y,X₁ and X₂ represented rice Cd,soil available Cd and soil p H,respectively?was obtained by automatic modelling.The accuracy of the equation reacheed 84.4%,and the significance level of each independent variable was less than 0.01.The regression coefficient had extremely significant statistical significance,and the equation was stable.Considering avoiding excessive alkalization of soil,weak acid fulvic acid microbial agent was introduced to remediate moderate-alkaline Cd-contaminated farmland soil besides biochar and sepiolite.It was hoped that soil remediation and fertilization could be simultaneously realized.For the safe use weak-alkaline Cd-contaminated farmland soil,remediation and fertilization should be considered simultaneously.The microbial agent of fulvic acid?0.03%?,biochar?0.46%?,sepiolite?0.12%? and their mixture?0.01%+0.15%+0.04%? were used as soil conditioners for in-situ remediation and fertilization.Soil available Cd decreased by 39.86%-71.33%,and wheat Cd decreased by 41.94%-87.10%.The wheat Cd decreased to 0.08 mg/kg with the remediation by the mixture,which was lower than the limit of 0.1 mg/kg of wheat Cd in GB 2762-2017.The highest yield of wheat is 7590 kg/hm².Fulvic acid significantly improved soil organic matter,nutrients and rhizosphere microorganisms;biochar significantly improved soil organic matter,and significantly inhibit wheat Cd and soil available Cd;sepiolite significantly reduced wheat Cd and soil available Cd;and the mixture was more balanced on soil remediation and fertilization.By reducing soil available Cd,inhibiting the transfer of Cd from wheat plant to grain,the mixed conditioner presented better effects on safe use weak alkaline soil remediation and fertility.There was a significant or extremely significant positive correlation between wheat yield and soil organic matter,soil available N and soil available P.Soil organic matter,soil nutrients and rhizosphere microorganisms jointly promoted the soil health.The correlation analysis showed that the key to simultaneous remediation and fertilization of Cd-contaminated weak alkaline soil was reduction of soil available Cd and increase of organic matter and nutrients.The modelling estimated that the relationship between soil available Cd and wheat Cd tended to be linear.The accuracy of linear model was 97.0%.