Effects Of Iron-based Humus On Soil Cadmium And Arsenic Availability And Rice Grain Accumulation

Restoration of heavy metal pollution,especially arsenic(As)and cadmium(Cd)combined pollution farmland soil and ensuring safe production of crops are significant issues to be solved urgently in China.Iron-based humus is a new type of soil heavy metal deactivator.In order to investigate the effect of iron-based humus on the bioavailability of cadmium and arsenic in contaminated soil and their content in the grain of rice,definitize the optimal application amount of iron-based humus in cadmium and arsenic-contaminated paddy field,follow expressions has been done.In this paper,four iron-based humus application rates of 0,1500,2250,3000kg/ha four treatments were set.Field plot experiments were carried out in Cd contaminative soil in Heng county of Guangxi(CK?Fe HS100?Fe HS150?Fe HS200)and Cd,As combined pollution farmland soil in Bingyang of Guangxi CK(c)?Fe HS100(c)?Fe HS150(c)?Fe HS200(c)to study the effects of different amounts of iron-based humus applied to rice fields contaminated by heavy metals on rice growth,the bioavailability of Cd and As in soil,and their absorption and accumulation in rice.The main research results are as follows:1.Adsorption experiments showed that the iron-based humus had an efficient adsorption effect on Cd and As,the adsorption capacity was more than 95%.2.Application of iron-humus had a role on rice yield,but the effect was not significant.The iron – humus treatments had little effect on the p H of soil polluted by Cd or Cd and As combined pollution,but it could reduce the Eh value of soil polluted by Cd and As combined pollution.3.Using iron-based humus could significantly reduce the content of Cd and As in soil pore water,and the content of Cd and As in soil pore water decreased with the increasing of iron-based humus application rate.In Cd-contaminated paddy fields,the Cd content in the pore water of Fe HS100,Fe HS150,and Fe HS200 treatments decreased by 4.9% ?25.6%,10.2% ?42.4%,and 20.0% ?47.5% during the four growth periods of rice;In the paddy fields contaminated with Cd and As Fe HS100(c),Fe HS150(c),and Fe HS200(c)treatments significantly reduced the Cd content in the soil pore water at the seedling stage and the mature stage,which was reduced by 18.1%,13.8%,20.5%,and 17.0% 39.1%,48.2%,respectively;at the same time,they significantly reduced the As content in the pore water of the tillering stage,respectively,by 68.0%,20.4% and 47.0%.4.The application of iron-based humus significantly reduced the available Cd and As content in the soil.In the Cd-contaminated paddy field,Fe HS200 treatment significantly reduced the soil available Cd content at the seedling stage,tillering stage,heading stage and mature stage,by 5.0% to 17.9%;The Fe HS150 treatment significantly reduced the effective Cd content in the soil at the tillering,heading and mature stages by 7.0% to 13.1%;the Fe HS100 treatment significantly reduced the effective cadmium content in the soil at the tillering stage,by 7.6%.In the Cd and As compound contaminated paddy fields,the treatments of Fe HS100(c),Fe HS150(c)and Fe HS200(c)generally significantly reduced the effective Cd content in the soil in each growth period of rice,with a decrease of 4.1% ?24.8%,0.0% ?15.9% and 4.0% ?13.3%;The application of iron-based humus could reduce the effective As content in the soil to varying degrees,but only Fe HS100(c)in the tillering stage and mature stage,and Fe HS200(c)in the seedling stage and tillering stage could significantly decrease As content in the soil compared with the control.5.The application of iron-based humus could reduce the content of total Cd,total As and inorganic arsenic in rice brown rice,and the decrease rate increases with the increase of the application amount.Among them,in Cd-contaminated rice fields,the cadmium content of brown rice treated with Fe HS100,Fe HS150,and Fe HS200 was significantly lower than that of the control,which was reduced by 39.1%,34.8% and 43.3% respectively;In the cadmium and arsenic compound contaminated paddy fields,the Fe HS150(c)and Fe HS200(c)treated brown rice cadmium content,and total arsenic content was significantly lower than the control,which was reduced by 30.2%,26.4% and 22.8%,29.7% respectively;the content of inorganic arsenic in brown rice treated with Fe HS100(c)and Fe HS200(c)was significantly lower than that of the control,and decreased by 8.8% and 10.2% respectively.6.Correlation analysis results showed that the content of Cd in brown rice was significantly positively correlated with the content of Cd in soil pore water and available Cd,indicating that the application of iron-based humus to reduce the accumulation of Cd and As in rice was mainly due to the reduction of Cd in soil pore water and available Cd.