Effects Of Silocon And Sulfur Fertilizer On The Uptake Of Cd&Cu By Rice In Contaminated Soil

Soil heavy metal pollution threats human health through the food chain.Soil contamination by heavy metals is serious in some areas of China.Rice is one of the main food crops.The decrease of heavy metal accumulation in the rice is the key point of the safety application of contaminted soil.Silicon which is an essential element of rice can promote the growth of rice and improve the resistance on stress.Sulfur can form sulfur-containing compounds in rice and influence heavy metal fractions in soil especially at flooding condition.In this paper,low Cd accumulated variety of rice was selected from20 varieties of new indentified rice through hydroponic experiment.Further,the effects of silicon fertilizer(sodium silicate)and sulphur fertilizer(sulphur powder)on the uptake of Cd and Cu by rice in polluted soil were studied by pot experiments.The safety application of heavy metal contamintaed farmland coul be promoted by the current research.The main results were as follows:(1)Hydroponics experiments showed that the accumulation of Cd in rice roots was positively correlated with NPT content,and Cd mainly distibuted in rice cell wall and soluble component.Based on the height,dry weight,growth health index and transfer factors(TFs)of rice,“Liangyou 289” was considered as the variety with low accumulation and high tolerance to Cd.(2)Pot experiment showed that PCs was the main-SH substance in the rice root while GSH was the main-SH substance in the rice stem at the panicle stage of rice growth.Single application of silicon fertilizer promoted the synthesis of NPT and PCs in rice root;Single application of sulfur fertilizer specially the medium and high dose of sulfur increase the concentration of GSH in rice stem.The concentration of NPT and PCs in rice root in the treatment with mixed application of silicon and sulphur fertilizers was lower than that in the control treatment.The effects of examined fertilizations on the content of NPT in rice stems were opposite to that in rice roots.(3)Pot experiment showed that Cd was mainly distributed in the cell wall in rice root at the panicle stage of rice growth.The examined fertilizations decreased the percentage of Cd in cell wall but increased the proportion of Cd in soluble fraction.The applicationof silicon and sulfur fertilizers tended to reduce the pecentage of Cu in root cell wall,but that in stems were promoted.(4)In pot experiment,the application of silicon and sulfur fertilizers increased the percentage of acid soluble Cd and decreased the percentage of residual Cd and acid soluble Cu in rhizosphere soil at the maturity stage of rice growth.The application of examined fertilizations promoted the immobilization of Cd on iron plaque of rice root surface in most cases,and the prevention of Cd by iron plaque on root surface was greater than that by rhizosphere soil.(5)In pot experiment,the order of Cd and Cu contents in rice organs was root >stem > leaf > brown rice > hull.The content of Cd in brown rice was not decreased in the treatment with mixed application of silicon and sulphur fertilizers was lower than that in the control treatment,but it was decreased by 30.1% in GS1 treatment.The content of Cu in brown rice declined by 5.03 mg/kg,3.05 mg/kg and 5.04 mg/kg in GS1,GS2 and GS3,respectively.(6)The single application of silicon and sulphur fertilizer just decreased the transformation of Cd from rice root to stem but increased the transformation of Cd from rhizosphere soil to Fe-plaque,from Fe-plaque to rice root and from stem to brown rice.The mixed application of silicon with low dose sulfur fertilizer declined the transformation of Cd from soil to brown rice through rice root and stem and the transformation of Cu from rhizosphere soil to rice root.This could be one of important reasons for the decrease of Cd and Cu accumulation in brown rice by GS1 treatment.