Effects Of Modifiers On The Morphology And Availability Of Cadmium In Paddy Soils

As the development of modern industry, the serious soil cadmium-pollution problem restrict the security and development of our country's rice production. Cd is a toxic heavy metal element, it's easy to enter human's body through food chain and harm human health. Because rice is the most important economic crops, so it's pressing to build reasonable pollution resistance system and safety rice production technical barrier of rice origin.After the "cadmium-rice" event, the cadmium contamination status of field and its controlling method in Hunan province had been the hotspot of social attention. Therefore, this experiment take the rice test base in Guiyang county, Hunan province as support. Studied the improving effect of addition of different proportion of manure and biochar to Cd-contaminated soil, included the effect to soil pH, available Cd, Cd form, soil microbial biomass, rice growth and rice Cd absorption. The results showed that:At mature period, soil pH increased a little, the soil pH of two rice increased 0.25 and 0.31 unit with the addition of 2% manure; The available cadmium of soils planted Mingzhusimiao all decreased, the decreasing amplitude was 28.0%-46.2%, high quantity of mixed fertilizer decreased the soil available Cd of Jiaxing-33 markedly.After three months, the Cd form of two rice had big difference, the Cd percent size order was exchangeable form>iron and manganese oxides combining form>carbonate combined form>residue form>organic combination form. With the treatments of M1, M2, M1C1 and M2C2, the soil Cd exchangeable form of Mingzhusimiao decreased markedly, they were 18.4%,18.5%,24.8% and 19.3% respectively, the exchangeable form of Jiaxing-33 decreased with no significant difference.All treatments increased soil ATP and biomass C concentration, M1, M2 and M2C2 increased the most, it was 803.7%,1121.2% and 629.6% to Mingzhusimiao and 301.1%,252.2%,379.3% to Jiaxing-33, it seems meliorant promoted the activity of microorganism. Treatment M2C2 and C1 promoted the growth of rice markedly, including plant height, root length and total biomass. Single addition of manure had the best effect on inhibition of root's absorption of Cd, Mingzhusimiao decreased 16.1% and 17.1%, Jiaxing-33 decreased 49.2% and 46.5%. The change of Cd in stem was opposite compared to root. All treatments promoted the absorption of Cd in rice husk. The Cd concentration in Mingzhusimiao rice decreased 11.6%,15.8%,10.3% and 5.50% with treatment M1, M2, M1C1 and M2C2. Other treatments increased the Jiaxing-33 Cd concentration in rice except M1 and M1C2, it showed that Jiaxing-33 had high resistance to Cd. In brief, manure addition had good improving effects on rice, such as increased soil pH, decreased the concentration of exchangeable Cd, increased the residue form, promoted the growth of rice, increased the plant biomass, inhibited the accumulation of Cd in rice.Ameliorant could repair Cd-contaminated soil, reduced the Cd absorption of rice, improved the rice growth dramatically. The two rice had different response to ameliorant, the lower Cd concentration of Jiaxing-33 showed high Cd resistance than Mingzhusimiao. Choose Cd resistance rice and cooperate with some ameliorant can decrease the Cd absorption of rice, decrease the transfer risk of Cd in food chain.