| The problem of heavy metal pollution has become increasingly serious in China.The report on the national general survey of soil contamination in China released in 2014 showed that the heavy metal pollution in soil exceeded the national standard with the site exceeding rate of 16.1%,in which the site exceeding rate of cadmium and arsenic were 7.0%and 2.7%,respectively.The site exceeding rates of cadmium and arsenic are the top two of heavy metal in soil exceeding the standard.Recently,the pollution of Cd-As has become one of the major problems in soil.Under flooded conditions during the whole growth period of rice,a pot experient was implemented to study the differences and correlations of soil properties and the accumulation of cadm ium and arsenic for two different varieties of rice（Weiyou 46 and Xiangwanyan 12）at different growth stages（tillering stage,booting stage,filling stage,mature stage）,with the application of Si fertilizer(0,20,40,80,160 mg·kg-1)in contaminated soil with high cadmium and low arsenic(1.5 mg·kg-1 of cadmium and 58.82 mg·kg-1 of arsenic).The main results were as follows:（1）Application of silicon fertilizer can significantly reduce the TCLP-cadmium content in paddy soils at tillering stage,booting stage,filling stage,and mature stage（P<0.05）;increasing the effective silicon content and soil pH value in paddy soils at tillering stage,booting stage,filling stage,and mature stage（p<0.05）.The effective arsenic content was significantly increased in paddy soils at tillering stage and maturity stage（p<0.05）.Under the same silicon treatments,the contents of cadmium and arsenic in Weiyou 46 were higher than that in Xiangwanyan 12 at the mature stage,respectively.（2）Under the conditions of silicon application,the cadmium content of brown rice in both varieties reached the national food pollutant limit standard at maturity;when the silicon application amount was 20 mg·kg-1,80 mg·kg-1 and 160 mg·At·kg-1,the inorganic arsenic content in brown rice of Weiyou 46 all dropped to below 0.2 mg·kg-1;when the silicon application rate was 80 mg·kg-1 and 160 mg·kg-1,Xiangwan Indica The content of inorganic arsenic in brown rice of No.12 rice also dropped below 0.2mg.kg-1,which meet the safety standard in the National Food Standards.Considering the contents of cadmium and arsenic in rice brown rice and rice yield,the silicon application rates advised was 20 mg·kg·1 for Weiyou 46,and 80 mg·kg-1 for Xiangwanxian12.（3）Under the conditions of experiment was setted,when the silicon application rate was 160 mg·kg-1,the silicon accumulation rate in Weiyou 46 rice at the booting stage was higher than that in other growth stages;When the silicon application rate was 40 mg·kg-1,the accumulation rate of silicon in Xiangwanxian 12 at the booting stage was basically higher than that in other growth stages.The accumulation rate of silicon in Weiyou 46 at different growth stages was basically higher than that of Xiangwanxian 12,respectively.（4）For Weiyou 46,soil available silicon can prevent the migration of rice cadmium and arsenic from root parts to subterraneous parts during the filling stage and maturity stage;soil pH can prevent the migration of rice cadmium and arsenic from root parts to subterraneous parts during the tillering stage and booting stage.During the booting stage,the transfer of silicon from roots to stems and leaves could hinder the migration of cadmium and arsenic from root parts to subterraneous parts.During the filling stage,the migration of silicon from stems and leaves to chaff could hinder rice removal of cadmium and arsenic from root parts to subterraneous parts.At the maturity stage,migration of silicon from stems and leaves to brown rice can impede the accumulation of arsenic from stems and leaves to brown rice.（5）For Xiangwanyan 12,soil available silicon and soil pH can impede the migration of cadmium and arsenic from root parts to subterraneous parts at the tillering stage;at the booting stage,soil available arsenic can prevent the migration of cadmium and arsenic from root parts to subterraneous parts.At the booting stage,the migration of silicon from roots to stems and leaves can hinder the migration of cadmium and arsenic from subterraneous parts to rice.During the maturity,the migration of silicon from stems and leaves to brown rice can prevent arsenic accumulation from stem and leaf to rice. |
