Effect Of Lime And Astragalus Sinicus On The Availability Of Cd In Paddy Soil With Different Rice Straw Returning Methods

Rice is the most important food crop in our country.With the increasing cadmium pollution in the paddy soil,the problem of rice cadmium is also becoming more and more serious,which seriously threatens food supply security and food safety.Therefore,how to control the cadmium pollution of rice and achieve its safe production has attracted much attention.With the increasing attention and concern of the whole society to environmental protection and ecological construction,coupled with the promotion of agricultural mechanization,the return of rice straw to cadmium contaminated paddy fields has been used widely used and increasingly popularized.However,how rice straw returing to soil affects the availability of cadmium in soil-rice system it is not clearly understood in cadmium contaminated paddy fields.Both application lime and Astragalus Sinicus are effective measures for the restration of Cd polluted paddy fields.However,it is not clear how the effect of application of lime and Astragalus sinicus on the availability of Cd in soil-rice system under different rice straw returning methods.It will provide theoretical and practical guidance for the safe production and utilization of rice straw in Cd polluted paddy fields by exploring the impact and its related mechanism of different straw returning methods and the application of lime or Astragalus Sinicus with different returning methodes on the availability of Cd in soil-rice systems.In this study,field trials and soil culture experiments were conducted to study the impact of straw returning(SR),straw leaving(SL),straw returning with lime(SRL),straw returning with Astragalus Sinicus(SRG),straw leaving with lime(SLL),and straw leaving with Astragalus Sinicus(SLG)on the availability of Cd and its related mechanism in Cd polluted paddy fields.The results of the experiments are as follows.1.By comparison with six treatments.Compared with SR,the effects of SL on the content of soil effective cadmium were not significant in different stages of rice growth.SRL compared with the SR can effectively reduce the available Cd content in soil,decreased by 61.17%?79.94%;From the beginning to the 56 d,SRG can increase the available Cd content in soil,in the late growth significantly reduce the available Cd content in soil;SLL compared with SL in each period of rice growth can effectively reduce the soil effective state content of cadmium,decreased by 30.16%?60.49%.SLG in rice growth before 56 d improves the cadmium content of soil effective state,reducing the cadmium content of soil effective state significantly in the late growth.Compared with SL,SLL can effectively reduce the soil effective state content of cadmium in each period of rice growth.SLG increases the content of soil effective cadmium in the first 56 d of rice growth,and significantly reduces the soil effective cadmium content in the later stage of growth.2.There was no significant difference in the amount of iron plaque on root surface between the six treatments.Compared with SR,the effects of SL on the content of DCB-Cd were not significant;SLL promote the fixation of iron plaque on root surface membrane on the Cd,it significantly increased the content of DCB-Cd,decreased by 65.44%;The effect of SRG on DCB-Cd was not obvious.3.By comparing the cadmium content of rice plants,the SR has significantly increased the amount of cadmium in all parts of the rice plant,the root,straw,rice husk and brown rice were increased by 23.20%,40.65%,33.84%and 32.78%respectively.Compared with the SR,SRL can obviously reduce the content of the cadmium in rice plants,the root,straw,rice husk and brown rice were reduced by 25.39%?60,32%?33.43%and 41.46%;SRG can significantly reduce the content of root cadmium,decreased by 26.04%.Compared with the SL,SLL significantly reduced the Cd content of root,straw and brown rice by 53.82%,64.89%and 33.71%respectively;SLG treatment of straw and rice husk was significantly increased by 37.53%and 29.59%respectively.4.Under flooded conditions,SL decreased the Cd content in soil solution at the first 42 d,and 56 d-98 d significantly increased the cadmium content in soil solution.Compared with SR,SRL and SRG significantly increased the content of Cd in soil solution during the training of 56d,which significantly reduced the Cd content of soil solution at 98 d,and the influence of other periods was not obvious.Compared with SL,SLL and SLG significantly increased the content of Cd in soil solution during the training of 56 d,which significantly reduced the Cd content of soil solution at 98 d,and the influence of other periods was not obvious.The Cd content of soil solution was significantly negatively correlated with the pH of soil solution;The content of Cd in soil solution was positively correlated with the content of Cu and NH4+-N in soil solution.