Effect Of Straw And Astragalus Sinicus Amendments On Availability Of Aresenic And Cadium In Fluvo-aquic Soil And The Practice In Rice

Straw and Astragalus sinicus are often used to improve soil heavy metal pollution, as common two kinds of organic material in the south of China. This research, using an admixture experiment of soil culture and pot culture, study the effect of single and combined application of rice straw and Astragalus sinicus on the bioavailability of Cd, As in soils and the accumulation in plants, revealing the mechanisms underlying decreasing the toxicities of Cd, As by the application of different ratio amounts of rice straw and Chinese milk vetch. Results as follow:1; Comparing with control, the single and combined application of rice straw and Chinese milk vetch both decreased the available Cd content at20d after the start of the treatment. For60d and120d, the single application of rice straw and Chinese milk vetch and the single application of Chinese milk vetch decreased the available Cd content respectively. Comparing with control, the single application of Chinese milk vetch causes an decrease of the content of exchangeable Cd and an raise of the contents of oxides, organic and residual Cd, and this performance was coincident at40d,80d,120d after the start of the experiment. As the prolongation of the experiment period, the ratios of exchangeable, oxide and residual Cd to the total Cd were decreased, while for carbonate and tight organic Cd were rising, and no significant differences were observed for organic bound Cd.2; The single and combined application of rice straw and Chinese milk vetch both could decreased the available As in Fluvo-aquicsoil. As the prolongation of the experiment period, the content of loose bound As was decreased, and for residual Cd first raised then decreased. The decrease of low available As was higher in single application of Chinese milk vetch than other treatments. These results show that the single application of Chinese milk vetch can decreased the available As in soils, but the efficiency was less than Cd treatment.3; Comparing with control, the application of Chinese milk vetch significantly increased the dry weight of rice straw, and for the dry weight of grains showed a tiny increase, these indicated that the application of Chinese milk vetch could decreased rice toxicity by As. The single and combined application of rice straw and Chinese milk vetch decreased the Cd contents in different parts of rice both in flooded and flooded-dry environments, and this tendency is greater in flooded environment. As the decrease of Cd contents in rice a key point, the application of Chinese milk vetch was better than other treatments under the flooded and flooded-dry environment with the decrease value of80%and70%respectively. However, the Cd content in rice grains was much higher in flooded-dry environment than in flooded environment. The Cd contents in rice grains was0.17mg/kg under the condition of the application of Chinese milk vetch in flooded environment, and this was significantly less than other treatments and less than the value of the China’s food cadmium limit standard.4、The single and combined application of rice straw and Chinese milk vetch both significantly increased As contents in straw, grain glume and brown rice in the conditions of the flooded and flooded-dry environment.Overall, results present here indicated that the single and combined application of rice straw and Chinese milk vetch caused an decrease of the Cd bioavailability in soils, and alleviated the inhibition of rice growth, yield and food safety by Cd. However, this tendency was not observed when grown in Fluvo-aquicsoils contaminated by As.