| Organic matter is the important factor that affect the activity and availablity of heavy metal in soil. Returning crop stocks and green manure to the field are the main methods to improve soil organic matter. In this study, soil incubation experiment was used to investigate the effect of straw and/or Astragalus sinicus amendments on activity and availablity of cadmium and arsenic in acid soil, and screened the proper additions of organic materials that could effectively reduce the activity of cadmium and arsenic. On this basis, pot experiment was conducted to investigate the effect of straw and/or Astragalus sinicus on rice growth and the concentration of cadmium or arsenic in different organs pf rice under cadmium or arsenic stress conditions. The main results were as following:1、Sample analysis in different cultivation period showed that supplying straw and/or Astragalus sinicus could significantly decrease the available Cd and Exch-Cd, but increased the Ox-Cd, SBO-Cd and Res-Cd, and the treatment with Astragalus sinicus alone was the best. With the extension of incubation time, the proportion of Res-Cd and SBO-Cd to total cadmium decreased gradually, but the proportion of WBO-Cd and Exch-Cd to total cadmium increased then decreased. With single Astragalus sinicus amendment, the proportion of Exch-Cd to total cadmium increased by13%from40to120days of incubation, and the increase extent was clearly lower than other treatments; meanwhile, the proportion of Res-Cd to total cadmium reduced by12%, and the reduction extent was also the lowest in all treatments2、Adding straw and/or Astragalus sinicus could reduce the activity of As in acid soil. With the extension of incubation time, the LB-As declined, the Ca-As and Org-As showed ascendant trend, the proportion of low activity of arsenic to total Arsenic with single Astragalus sinicus amendment was higher than other treatments.In sum, the activity of Arsenic could be reduced by adding Astragalus sinicus in acid soil, but the effect was not significant than cadmium.3、Pot experiment showed that compared with the control, adding straw and/or Astragalus sinicus could markedly increase the productive tiller and grain yield of rice, and reduce the toxicity of cadmium and arsenic to rice. Suppying straw and/or Astragalus sinicus could reduce the cadmium concentration in the straw, husk and brown rice regardless of water management regime. For reducing the cadmium concentration in brown rice, compared with the control, the Cd concentration in brown rice reduced by70%with Astragalus sinicus addition alnoe, which was the best in all treatments under flooded conditions. The Cd concentration in brown rice reduced by80%with both Astragalus sinicus and straw addition, which was the best in all treatments under alternation of drying-wetting conditions, but the cadmium concentration in brown rice under alternation of drying-wetting conditions were remarkably higher than those corresponding treatments under flooded conditions. The cadmium concentration in brown rice was0.16mg kg-1under flooded conditions with Astragalus sinicus amendment alone, which was the lowest in all treatments, and was lower than the national limiting standard of cadmium in food.4、For arsenic, under flooded conditions, the arsenic concentration was As+G≥As+S≥As+G+S>CK+As70in the straw, As+G+S> As+G≥As+S>CK+As70in the husk, and As+S≥As+G≥CK+AS70≥As+G+S in the brown rice. Under alternation of drying-wetting conditions, the arsenic concentration was CK+AS70>As+G≥As+S≥As+G+S in the straw, As+G≥As+G+S≥As+S≥CK+As70in the husk, and As+S> CK+As70≥As+G≥As+G+S in the brown rice.This study demonstrates that returning straw and/or green manure (Astragalus sinicus) are effective measures that can be used to reduce the activity and availablity of cadmium in acid soil, and alleviate the effect of cadmium stress on rice growth, yield and food safety; But they are inadvisable for reducing arsenic stress to rice in acid soil. |
PDF Full Text Request