Effect Of Mineral Silicon And Organosilicone Fertilizer On Chemical Forms Of Cadmium And Lead In Soil And Their Accumulation In Rice

Food safety arising from the contamination of cadmium(Cd)and lead(Pb)in some of the Chinese farmland soils has received ever-increasing attention.It has been well-documented that mineral silicon can be effectively used for immobilizing heavy metals(HMs)in soil to reduce HMs accumulation into rice grain.However,whether organosilicone is also effective in immobilizing HMs in soils and inhibiting root-to-grain transport of HMs and what is the difference in this regard between mineral silicon and organosilicone fertilizer remain unclear.For this,we compared the differences in immobilizing Cd and Pb between mineral silicon manufactured from feldspar and organosilicone fertilizer by investigating the chemical forms of Cd and Pb in a paddy soil amended with Cd or Pb using soil incubation experiment.Meanwhile,at the mature stage we investigated the effects of mineral silicon and organosilicone fertilizer on the contents of Cd,Pb and silicon in soil and rice grown on a potted paddy soil contaminated experimentally with either single Cd and Pb or compound Cd and Pb.The main results obtained are presented as follows:1.In the incubation experiment with soil amended with single Cd and Pb,the soil p H increased significantly by application of mineral silicon and organosilicone fertilizer.But the soil redox potential(Eh)decreased significantly.The content of soil available Cd and Pb was decreased by addition of mineral silicon fertilizer by 77.4% and 96.9%,as compared to 38.7% and 88.4% by addition of organosilicone fertilizer.2.In the pot experiment with soil contaminated with single Cd and Pb,firstly,we found that the biomass of brown rice in rice was increased by 22.1?29.9% by application of mineral silicon fertilizer at a rate of 6.67 g/pot compared with Cd or Pb treatment only(p<0.05).Secondly,addition of mineral silicon fertilizer to single Cd contaminated soil decreased Cd content in root,straw,husk and brown rice grain by 26.5?45.3%,20.8?40.4%,47.7?76.2% and 34.5?54.6% respectively compared with Cd treatment only(p<0.05),while addition of organosilicone fertilizer to single Cd contaminated soil decreased Cd content in root,straw and husk by 20.3?25.4%,12.9?16.3% and 47.2?51.3% respectively compared with Cd treatment only(p<0.05).The content of Cd in brown rice decreased by 38.1% only when organosilico ne fertilizer was applied at a rate of 6.67 g/pot(p<0.05).In contrast,addition of mineral silicon fertilizer to single Pb contaminated soil decreased Pb content in straw and husk by 29.2?48.5% and 21.7?60.9% respectively compared with Pb treatment only(p<0.05),while addition of organosilicone fertilizer to single Pb contaminated soil decreased Pb content in straw and husk by 16.1?24.7% and 24.9?38.6% respectively compared with Pb treatment only(p<0.05).The Pb content of brown rice was 22.8?54.8% lowe r in the treatment with Pb with mineral silicon fertilizer than in the treatment with Pb without mineral silicon fertilizer,but no significant impact on the content of Pb in rice root and brown rice grain was observed when organosilicone fertilizer was added.There was no significant effect on Pb content in rice root neither when mineral silicon fertilizer was added.3.In the pot experiment with soil contaminated experimentally with compound Cd and Pb,firstly,we found that addition of either mineral silicon or organosilicone fertilizer did not increase the biomass of each part of rice plants significantly.Secondly,the application of mineral silicon fertilizer decreased Cd content in root,straw and husk by 24.1?35.3%,8.5?19.8% and 35.3?70.6% respectively compared with compound Cd and Pb treatment only(p<0.05).Only when mineral silicon fertilizer was applied at a rate of 6.67 g/pot,did the Cd contents of brown rice decrease by 49.2% compared with compound Cd and Pb treatment(p<0.05),while the application of organosilicone fertilizer decreased the Cd contents of rice root by 18.4?19.5%(p<0.05).Cadmium content in straw and husk were decreased by 8.9% and 20.6% by organosilicone fertilizer added at a rate of 6.67 g/pot(p<0.05),while no impact of organosilicone fertilizer on the content of Cd in brown rice was noted.Meanwhile,the application of mineral silicon fertilizer decreased the Pb content in straw,husk and brown rice by 17.1?37.4%,64.7?76.3% and 62.0?63.8% respectively compared with compound Cd and Pb treatment only(p<0.05),but there was no significant effect on the Pb content of root in rice.In contrast,the application of organosilicone fertilizer decreased Pb content by 17.4?26.2% in husk,and by 13.1% in straw at the rate of 6.67 g/pot(p<0.05),but the application of organosilicone fertilizer had no significant effect on the Pb content of root and brown rice.4.In the pot experiment with soil contaminated with single and compound Cd/Pb,firstly,Si content in rice straw increased significantly only when mineral silicon fertilizer was added,while the application of organosilicone fertilizer had no effect on Si content in rice straw.The application of both mineral silicon and organosilicone fertilizer significantly increased the so il p H.The addition of mineral silicon fertilizer increased soil available Si content,while organosilicone fertilizer had no impact.In addition,the application of mineral silicon and organosilicone fertilizer decreased the available Cd content in soil and led to the transformation of chemical speciation in single Cd and compound Cd/Pb contaminated soils.By contrast,adding mineral silicon fertilizer significantly decreased the available Pb content,while the application of either mineral silicon or orga nosilicone fertilizer did not significantly impact the transformation of soil chemical speciation of Pb in single Pb and compound Cd/Pb contaminated soils.The effect of mineral silicon fertilizer on transformation of heavy metals was better than that of organosilicone fertilizer,and better with increasing of fertilizer rate applied.