Effect And Mechanism Of Silicon-Rich Rice Husk Ash On Transport Of Cd And As In Paddy Field System

The combined pollution of cadmium(Cd)and arsenic(As)in paddy fields affects the safe production of rice and endangers human health.Silicon(Si)plays an important role in reducing Cd and As uptake in brown rice.Rice husk is a good source of silicon fertilizer because of its high Si content.In this study,Si-rich husk ash was prepared with husk as raw material,and the regulatory effect and mechanism of Si-rich husk ash on Cd and As migration and transportation in paddy field system were studied through pot and field experiments.The main results are given as follows:(1)Rice husk ash(H600),which is burned at 600℃ and leached by dilute nitric acid,has rich functional groups,which can effectively reduce the availability of Cd and As in soil.Soil ripening test showed that H600 could lower exchangeable Cd and As contents by 72.3%and 8.9%,respectively.The structure characterization analysis shows that H600 has the characteristics of high avaiable Si content,large specific surface area,rich functional groups of Si-O-Si,-OH and-COOH.(2)The application of H600 increased the available Si content in rhizosphere soil of rice,decreased the bioavailability of Cd and As in soil,and decreased their bioavailability,H600 was applied to soil with Cd of 2.6 mg-kg-1 and As of 90.5 mg·kg1 and rice Huanghuazhan,Xiangwanxian 13 and Longyou 4945 were planted in pot.The application of 0.5%-2%H600 increased the available Si content of rhizosphere soil by 7.4%-41.4%,and decreased the soil organic matter content by 5.0%-26.3%.The contents of CaCl2 extractable state,TCLP extractable state and acid extractable state of Cd in soil decreased by 7.8%-18.7%,7.4%-18.7%and 0.9%-16.7%,respectively.The contents of exchangeable state and TCLP extractable state of As also decreased by 6.1%-47.2%and 4.3%-26.7%,respectively.Correlation analysis showed that there was a negative linear correlation between soil available Si content and three extractable Cd contents.(3)The application of H600 could promote the transformation of soluble Cd in rice rhizosphere soil to insoluble state,and reduce the migration ability of Cd in soils.Pot experiments showed that the contents of acid extractable Cd and Fe-Mn bound Cd in rhizosphere soil of rice Huanghuazhan,Xiangwanxian 13 and Longyou 4945 decreased to varying degrees with the application of 0.5%-2%H600,and the contents of residual Cd in rhizosphere soil of Xiangwanxian 13 and Longyou 4945 increased by 9.8%-23.5%and 5.9%-28.1%,respectively.(4)The application of H600 could reduce the contents of Cd and As in each part of the three rice varieties,and increase the iron film content on root surface and Si content in each part of rice.0.5%-2%H600 and 1%H600 could reduce the Cd content in Longyou 4945 and Xiangwanxian 13 brown rice to below 0.2 mg·kg-1,respectively,while 2%treatment could reduce the inorganic As content in Huanghuazhan brown rice to below 0.2 mg·kg-1.In addition,Si/Cd and Si/As ratios in all parts of the three rice varieties increased,and there was a negative linear correlation between Fe content in iron film on root surface and As content in root.(5)Application of H600 in the field and planting rice Huanghuazhan,soil available Cd and As content decreased,consistent with the pot experiment.The Cd content of brown rice decreased from 0.46 mg·kg-1 to 0.25 mg·kg-1 and the total As content of brown rice decreased from 0.16 mg·kg-1 to 0.13 mg-kg-1 under 0.25%-1%H600 treatment.