| With the accelerating process of industrialization and urbanization,the increasing discharge of waste water,waste gas and waste residues,the abuse of pesticides and fertilizers,and sewage irrigation have made soil cadmium pollution more serious and even affected human health.With the "Soil Pollution Prevention Action Plan"promulgated by the State Council in 2016,soil heavy metal pollution has received widespread attention,and the requirements for remediation of heavy metal pollution in farmland have become more stringent.Therefore,it is necessary to find cost-effective and practical agronomic control measures for polluted farmland repair.In view of this,this article carried out restoration work on a mildly cadmium-contaminated farmland affected by an electronics factory in a village in Dainan Town,Xinghua City,and carried out two consecutive years of in situ immoblization community experiments to explore the effects of water management,silicon fertilizer and their combinations(2018)as well as water management,amendments,different rice varieties and their combinations(2019)on soil pH,available Cd content in the soil,rice enrichment of Cd,and rice agronomic traits.At the same time,the screening of heavy metal mutants in rice was carried out.Through the determination of heavy metal elements in rice grain,rice mutants with low and low content of heavy metals were selected from 403 rice grains tested.The main conclusions are as follows:(1)For screening of low-accumulation varieties of Cd,we selected seven japonica rice varieties.including Nanjing 9108,Zhendao 99,Huaidao 18,Huaidao 5,Yangyujing 3,Yanjing 15,Fengjing 3227 and two previously identified low cadmium accumulation indica rice varieties Longxiangyou 130 and Shenyou 957.In terms of yield,the highest rice yield is Nanjing 9108.up to 582.8 kg/mu;the lowest yield variety is Longxiangyou 130.which is 3 16.4 kg/mu.In terms of the Cd content in brown rice,none of the nine rice varieties exceeded the national food safety standard(GB 2762-201 7.0.2 mg/kg).The highest Cd content was the local main variety Nangjing 9108,which was 0.18mg/kg.the lowest is Zhendao 99.which is only 0.039 mg/kg.and the remaining 8 varieties are lower than Nangjing 9108 and all reach significant differences.(2)Field try was carried out to compare the effect of "Zhongdi Pure Soil" soil amendment and the Si-Ca-K-Mg fertilizer in remediation of mild Cd contaminated farmland.There was no significant difference in the seed setting rate,thousand-grain weight,yield per plant,and yield of rice treated with "Zhongdi Jingtu" soil amendment and the Si-Ca-K-Mg fertilizer.Both of them can increase the soil pH,reduce the soil available Cd content,and inhibit the absorption of Cd by rice,which are significantly different from the control.The application of soil amendments increased the soil pH by 0.59 units,the soil Cd availability was reduced by 19.50%,and the brown rice Cd content was reduced by 35.00%;the application of the Si-Ca-K-Mg fertilizer treatment increased the soil pH by 0.41 units,and the extractable content of Cd in the soil decreased by 22.74%and the Cd content of brown rice decreased by 36.50%.(3)The rice variety tested in 2018 was the local main cultivated variety Nanjing 9108 in Xinghua City.The content of Pb,As,Cu and other heavy metals in the soil do not exceed the standard.In this field test,water management,silicon fertilizer and their combined treatment were used to remediate mild Cd contaminated farmland.Flooding during the whole growth period has a slightly negative effect on the seed setting rate,thousand-grain weight,and yield per plant of rice,but there is no significant difference.The application of silicon fertilizer can play a certain role in increasing yield.Flooding during the whole growth period and application of silicon fertilizer can increase the soil pH and inhibit the absorption and enrichment of Cd in rice.Among them,the application of silicon fertilizer under flooding conditions during the whole growth period is the best strategy,which reduced grain Cd by 20%.(4)In the in situ immoblization experiment,the main varieties were Nanjing 9108 and Nanjing 5718 in 2019.There were no significant differences between Nanjing 9108 and Nanjing 5718 in terms of rice agronomic traits,yield,and Cd accumulation in rice grains.The combined use of organic and inorganic combined application of amendments has the most obvious effect of increasing yield,which results in an increase of 7.31%and 6.20%,respectively,in Nanjing 9108 and Nanjing 5718.Flooding during the whole growth period.amendments and their combinations can increase the soil pH value by 0.04-0.47 units.Flooding during the whole growth period,combined application of organic and inorganic materials,and amendments can reduce the available Cd content in the soil and inhibit the absorption and accumulation of Cd in rice.The best remediation effect reduced the extractable Cd content of the soil by 22.18%-31.82%,and the Cd content of brown rice of Nanjing 9108 and Nanjing 5718 decreased by 51.76%and 41.34%,respectively.(5)The rice mutant library constructed by EMS mutagenesis in the background of Zhonghua 11 was screened for the extreme accumulation of heavy metals in the grain.It was found that among the 403 screened mutants,the heavy metal content in the grains had a larger variation range than that of wild type.30 and 16 mutants were isolated as high or low Cd accumulation mutants,respectively.19 and 4 mutants were isolated as high or low As accumulation mutants,respectively.20 and 6 mutants were isolated as high or low Ni accumulation mutants,respectively.21 and 11 mutants were isolated as high or low Cu accumulation mutants,respectively.16 and 18 mutants were isolated as high or low Zn accumulation mutants,respectively.In summary,in the mildly Cd-contaminated farmland of Dainan Town,Xinghua City,the application of the whole-grwoth-stage flooding,silicon fertilizer,organicinorganic combined application,amendments,and joint control measures with lowaccumulation Cd rice varieties can effectively reduce the accumulation of rice brown rice Cd without yield penalty and thusensure the quality and safety of rice.The isolation of rice muttants with high or low accumulation of heavy metal in grains from a rice mutant library generated by chemical mutagens facilitates the coloning the underlying mutated genes and the breeding rice varieties with low heavy metal accumulation and thus is of great significance for ensuring rice quality and safety. |
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