| Soil is the resource of human survival.It is the basis of agricultural production and social and economic development.In recent years,due to unreasonable industrial and agricultural production and management,soil in China has been polluted by various degrees of heavy metals.It not only reduces the quality of soil,but also affects people’s dietary safety and endangers human health.The heavy metal pollution in soil in China is mainly light and moderate.The application of bio-organic fertilizer to soil can effectively repair heavy metal pollution.In order to study the mechanism of the effect of bio-organic fertilizer on cadmium(Cd)soil pollution,a long-term experiment on Cd pollution was conducted in Beishan Town of Changsha,Hunan province.The bio-organic fertilizer was applied into the experimental field at once,the effects on the Physical and chemical properties of red paddy soil,rice yield,Cd morphology transformation in soil,cd enrichment and transfer of rice organs were studied.The correlation between the change of soil physical and chemical properties and the Cd content of rice grain was studied by correlation analysis and diameter analysis.The main component analysis method was used to study the effect of bio-organic fertilizer on soil comprehensive fertility.The results of this study can provide scientific basis for bio-organic fertilizer in repairing Cd-contaminated red paddy soil,ensuring food security and improving soil fertility in research areas.The study results were as follows:(1)Bio-organic fertilizer could significantly reduce the bulk density and improve the total porosity of the soil.By adding bio-organic fertilizer at one time,the soil bulk density decreased by 2.42%to 9.68%at maturity period after one year.Meanwhile,the total soil porosity increased by 2.45%to 8.65%.In addition,with the increase of the amount of bio-organic fertilizer application,the physical properties of soil,such as soil moisture content,field capacity and available water content,all increased,and rice yield increased by 4.56%to 22.69 percent.(2)Bio-organic fertilizer could improve the soil pH value and increase cation exchange capacity.Compared to before fertilization,after one-time application of bio-organic fertilizer,soil pH and cation exchange in the first year of rice ripening were increased by 3.69%to 24.95%and 3.26%to 30.83%respectively.Soil organic matter,total nitrogen and total phosphorus content can be increased by 8.08%to 41.28%,5.26%to 14.91%and 3.26%to 11.54%,and soil ammonium nitrogen,nitrosand nitrogen and effective phosphorus content increased by 27.01%to 64.40%,13.32%to 79.92%and 7.62%to 34.91%respectively.(3)The distribution of Cd content in different forms in red soil rice soil is acid-soluble form>reducible form>residual form>oxidizable state.The soil acid-soluble Cd content was reduced after the application of bio-organic fertilizer in the experimental area.The content of reducable and oxidable Cd increased,and there was no significant change in the content of residual Cd.The soil acid-soluble Cd content decreased by 5.41%to 22.42%,the reducable state Cd content increased by 10.40%to 28.22%,the oxidizing Cd content increased by 27.63%to 59.21%,and the residual Cd content increased significantly(P>0.05)in the first year of rice ripening.(4)The Cd content in rice roots,stalks,leaves and grains after the one-time application of bio-organic fertilizer was significantly reduced with the increase of the amount of bio-organic fertilizer application.Compared to the control group(CK)in the first year of rice ripening,the Cd content of the roots,stalks,leaves and seeds treated by Y40 decreased by 24.42%,46.14%,26.56%and 44.82%respectively,and the rice root enrichment coefficient decreased by 15.03%to 17.62%,the root system-stem stalks,stalks-the coefficient of inter-grain transport also decreased significantly with the increase of the amount of bio-organic fertilizer application.The above results can be attributed to the application of bio-organic fertilizer to reduce the absorption of rice root system to Cd,reducing the transport of Cd in the plant body.(5)The three indicators of soil pH,cation exchange and organic matter content showed a significant negative correlation with the content of acid-soluble Cd(P<0.01),while obvious positive correlation was shown with the reduced,oxidized and residual Cd content(P<0.05).The path analysis showed that the soil acid-soluble Cd content had a direct positive effect on the grain Cd content.The Principal component analysis showed that the physical and chemical properties of soil can be divided into the first,second and third main components,and the contribution rates of the three main components were 63.83%,16.44%and 7.90%,respectively.When the amount of bio-organic fertilizer applied is 40 t/hm2,the comprehensive fertility level of soil reaches the highest. |
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