Effects Of Different Amendments On Cd And Pb Immobilization In Weakly Acidic Soil-rice System

Cadmium(Cd)and lead(Pb)pollution of cultivated soil is a global environmental problem.Applying alkaline amendments such as lime on acidic soil is not only a traditional measure to improve soil acidity,but also a conventional technique to immobilize heavy metals(such as Cd and Pb).For the soils of which the acidity has been increased to weakly acid,it is not clear whether the alkaline amendments are still effective in immobilizing the soil heavy metals.In view of this,field experiments were conducted on paddy soils with weak acidity of Cd and Pb pollution(initial pH value of soil was 6.18 and 5.45,respectively)in Xinluo District,Longyan City and Zerong County,Ningde City,to study the passivation effects of 8 commonly used amendments and their combinations on paddy soil Cd and Pb,and to explore the passivation mechanism.In order to provide the basis for soil risk control of polluted cultivated land.The main findings are as follows:(1)The pH value and organic matter content of soil treated with amendment ranged from-4.3% to 9.1%,but most of them did not reach significant level.In general,the addition of amendments promoted the change of soil Cd and Pb from exchangeable and Fe-Mn oxides to organic and residual states.Partial amendment treatment reduced the effective amount of Cd and Pb in soil,but the overall reduction effect was not obvious.The treatment of sepiolite,organosilicon fertilizer and zeolite +biochar decreased the available Cd content in two soils,and the treatment of hydrated lime,zeolite,attapulgite,organosilicon fertilizer and zeolite +biochar decreased the available Pb content in two soils.(2)In the experiment in Xinluo District,except for organosilicon fertilizer,other amendments can reduce the Cd content of brown rice,the decrease is between 4.9%～66.7%;In the experiment in Zherong County,different amendments had better effect on reducing Pb content in passivated brown rice.The treatment of limestone powder,hydrated lime and zeolite all reduced the Pb content of brown rice by 5.6%～68.2%,while the treatment of organosilicon fertilizer,sepiolite + biochar did not reduce the Pb content of brown rice.(3)Except for the treatments of limestone powder,zeolite and zeolite+ biochar,other amendments increased rice yield by 0.2%～25%,but the increase did not reach a significant level.(4)The amount of iron plaque formed on the root surface was positively correlated with the content of Cd in the iron film,but without significant difference.The iron plaques of some treatments were significantly and positively correlated with the content of Pb in the iron plaque.Amendments reduced the amount of iron plaques,and then reduced the content of Cd and Pb in the iron plaque.Organosilicon fertilizer did not reduce the content of Cd and Pb in the iron plaque.(5)The accumulation of Cd and Pb in brown rice was mainly affected by the transfer of Cd and Pb from roots to stems,and from leaves to brown rice.Amendment treatment inhibited the transfer of Cd and Pb from roots to stems and leaves to brown rice,thereby reducing the contents of Cd and Pb in brown rice.(6)In Cd contaminated soil,hydrated lime,sepiolite,zeolite + biochar can be preferred as amendments.In Pb polluted soil,hydrated lime,limestone powder and zeolite can be preferred as amendments.