| Hunan is the largest rice production province in China,and Changzhutan area is a national pilot area for the comprehensive restoration and treatment of heavy metal contaminated farmland.The success or failure of the pilot area is related to the treatment trend of over 100 million mu of contaminated farmland.In addition,with the rapid development of agricultural modernization,the treatment of heavy metal contaminated farmland soil is urgent.The heavy metal cadmium(Cd)pollution and its complex pollution with various heavy metals seriously affect human health,food security and social development.In view of the farmland polluted by moderate and mild heavy metal Cd,the basic application of passivating agent is one of the effective measures at present.It reduces the chemical activity and biological effectiveness of Cd by curing/stabilizing Cd in the soil,so as to reduce the absorption of Cd by plants in the soil and realize the safe production and utilization of farmland.In hunan zhuzhou positioning test platform,this paper studies the continuous use different passivation agent(lime,biochar,light burning powder,fulvic acid+light burning powder,silicon fertilizer and silicon fertilizer+light burning powder)for cropping field soil physical and chemical properties and the influence of different form the Cd content,and analyze the Cd content in different form and direct relationship between rice Cd.The research results of this paper are as follows:(1)There was no significant difference in soil Cd content between different treatments in early and late rice maturation stages.During the whole growth period of rice,the content of effective Cd in the soil showed a downward trend,and the content of Cd in different forms during the maturity period was from high to low,which were exchange state,carbonate binding state,iron and manganese oxidation state,organic binding state and residue state,respectively.Compared with the non-application of passivating agent,the content of Cd in soil exchange state could be effectively reduced by using different passivating agents in early and late rice,while the content of Cd in soil carbonate bond state,fe and mn oxidation state and residue state were all increased.The effective content of Cd in soil from tillering stage to mature stage of early and late rice decreased by 15.1%and 16.1%on average,and the content of exchangeable Cd in soil decreased by 43.9%and 39.4%,respectively,compared with that without passivation treatment.(2)During the whole growth period of early and late rice,the soil pH value was increased by 2.56 and 2.98 units on average when the soil pH value of early and late rice was increased by lime treatment compared with that of no passivation.And the soil Eh goes down.There was no significant difference in soil EC in the whole growing period of early rice(P>0.05),while in late rice,the soil treated with silicon fertilizer+light burning powder was higher,and the average increase from tillering stage to maturity stage was 102.4%compared with that without passivation treatment.During the whole growing period of early rice,there was no significant difference in soil CEC treatment with different passivation agents,while there was significant difference in soil CEC treatment with different treatments from booting stage to maturation stage of late rice,in which the average increase of 5.39 cmol·kg-1 was achieved when light burning powder was applied to tillering stage to maturity stage compared with no application.In addition,the contents of alkali-hydrolyzed nitrogen,available phosphorus and available potassium in soil treated with different passivating agents in early and late rice were improved compared with those without passivating agent,and the increase was greater when treated with light burning powder and silicon fertilizer+light burning powder.(3)Compared with the treatment without passivation,the plant height and tiller number of rice treated with lime were reduced;However,the plant height,tiller number and SPAD of rice could be improved by biochar treatment,and the difference between treatments was not significant.The photosynthetic characteristics of functional leaves of early and late rice were reduced when lime was applied,while Pn,Gs and Tr of functional leaves and leaves of other treatments were increased,and Ci was reduced.The panicle length,1000-grain weight and seed setting rate of double-cropping rice were all reduced after application of lime,and the rice yield was significantly reduced(P<0.05).There was no significant difference between the panicle length and rice yield of other double-cropping rice treatments and the treatment without passivation,but the 1000-grain weight,the number of solid grains and the seed setting rate were all increased.(4)Cd content of root system in early tillering stage and late tillering stage of rice treated with passivating agent was lower than that without passivating agent,and it was reduced by 77.4%and 71.6%when lime was applied,respectively(P<0.05).In the mature stage of double-cropping rice,the Cd content of the plants in each treatment showed as:no passivation agent>biochar>silicon fertilizer>xanthoic acid+light burning powder>silicon fertilizer+light burning powder>lime,among which the early and late rice were treated with silicon fertilizer+light burning powder,the reduction was 57.5%and 94.2%respectively.In addition to biochar treatment,the content of Cd in early and late rice ear treated with different passivating agents was significantly lower than that treated with no passivating agent(P<0.05).The content of Cd in double cropping rice rice was the lowest with lime,and the content of Cd in brown rice treated with light burnt powder and silicon fertilizer+light burnt powder reached the national food safety standard.Correlation analysis showed that the content of effective Cd in soil was positively correlated with the content of exchangeable Cd in soil(P<0.01),while it was negatively correlated with the content of carbonate binding Cd in soil(P<0.01).The content of Cd in brown rice was positively correlated with the content of available and exchangeable Cd in soil,but negatively correlated with other forms,and the difference in late rice was significant or extremely significant(P<0.05 or P<0.01). |
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