| The in-situ remediation technology of heavy metals in soil is widely used in our country.The return of organic materials and the application of lime is an improvement on this remediation technology.It can not only reduce heavy metal pollution in farmland,but also improve soil quality and reduce the application of agricultural fertilizers.It is of great significance to ensure the safety of agricultural products and the safe use of farmland contaminated by heavy metals.The experiment used organic materials-rice straw and milk vetch in the field combined with lime to carry out field experiments on Cd-contaminated paddy soil to explore the impact of lime and organic materials on the migration of cadmium in the soil-rice system.The main conclusions are as follows:（1）Single application of Chinese milk vetch（CMV）and rice straw（S）promoted the absorption and accumulation of Cd by rice,while the application of lime（L,SL and CMVL）reduced the absorption and accumulation of Cd by rice.Compared with CK,the Cd content of rice treated with L,SL and CMVL in the three seasons was significantly reduced,with a decrease of 51.99%～65.10%,89.19%～89.69%,and 93.65%～94.32% respectively;the Cd content of rice treated with S and CMV appeared significant The increase in the number has increased by 52.84%～58.68%,48.77%～69.95%and 29.64%～35.67 respectively.Treatment L,SL and CMVL all showed a gradual decrease in the three seasons.The Cd content of rice after continuous application of 300 kg acres of lime for the second cropping was lower than the Cd limit of rice(0.2 mg kg-1)in the National Food Safety Standard（GB2762-2017）.（2）Single application of organic materials for the second season inhibited the formation of rice root surface film and reduced the adsorption of cadmium on the root surface film.Lime alone or combined with organic materials inhibited the formation of rice root surface film and reduced the adsorption of cadmium on the root surface film. Compared with CK,DCB-Fe in the first season of S and CMV treatments were significantly increased by 80.28%and 38.27%（p<0.05）,and the content of DCB-Fe after the second season was reduced by 18.40%-20.71%,respectively.Applying L,SL and CMVL The content of DCB-Fe decreased by 23.18%～58.61%,33.39%～57.59%and 30.69%～47.33%respectively after two seasons.Compared with CK,DCB-Cd in the first quarter of S and CMV treatments were significantly increased by 60.45%and 232.61%（p<0.05）,while after the second quarter,the DCB-Cd content was reduced by 11.11%～37.79%and 22.97%～45.04%,respectively,L,SL and CMVL treatments reduced DCB-Cd content by 32.88%～87.36%,18.33%～87.59%and 12.76%～83.77%,respectively.Single application of organic materials promotes the transport of cadmium from the root Fe-Mn plaque to roots and promotes the accumulation of cadmium content in rice.Single application and combined application of lime inhibits the transport of cadmium from roots to rice.（3）The application of lime will increase the pH of the soil and reduce the availability of heavy metals in the soil,thus inhibiting the formation of the root Fe-Mn plaque,reducing the absorption efficiency of heavy metals by rice,and ultimately reducing the content of cadmium in rice.（4）The application of organic materials will promote the increase of the relative abundance of the dominant flora,while the continuous single application and combined application of lime will reduce the number of microbial communities.The number of communities treated by continuous single application of milk vetch and milk vetch combined with lime and lime treatment were all at a relatively high level.The physical and chemical properties of soil have an important influence on functional microorganisms.The continuous application of lime increases the pH and strengthens the effect of microbial stress.The functional flora is related to the formation of the root Fe-Mn plaque.Microbes may prevent the absorption and accumulation of heavy metals on the root Fe-Mn plaque. |
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