Remediation Effect Of Green Manure And Straw Return On Cadmium-contaminated Paddy Soil

With the continuous development of modern industry and agriculture,the soil cadmium pollution in rice fields in the south has become increasingly serious,which has brought problems such as soil degradation and excessive cadmium content in rice grains,resulting in serious harm such as reduced rice production and no harvest,further affecting human health and causing harm to the people.The safety of life and property has created huge hidden dangers.Therefore,finding suitable soil cadmium pollution control measures in southern paddy fields is of great significance for safe and green rice production.Pot experiments were carried out in the potting farm of Huazhong Agricultural University,Hongshan District,Wuhan city,Hubei Province,from 2019 to 2021.The planting mode of rice-green manure rotation was used.The differences in rice yield and nutrient uptake,changes in soil physicochemical properties and enzyme activities,dynamic changes in soil cadmium activity,and differences in rice cadmium content and accumulation under the condition of combined application of physical modifier lime.The effect of pollution control and the ability to improve physical and chemical properties,as well as the contribution to the safe and green production of rice,provide a technical basis for green manure to participate in the treatment of cadmium-contaminated paddy soil in southern China.The main conclusions are as follows:(1)The separate returning of straw and green manure on cadmium-contaminated paddy fields cannot effectively increase the yield of rice and paddy,but the combined returning of the two can effectively increase the yield of paddy rice,which increased by 27.0% and35.6% respectively in two years;physical modifiers Lime had a significant yield-increasing effect only in the first year,and the yield-increasing effect gradually weakened with the increase of planting years.green manure,straw return and lime application returning increased the nitrogen accumulation of rice by 20.5%,18.5% and28.6%,34.1%,respectively.Straw could also promote the accumulation of potassium in rice.The physical amendment lime would lead to an increase in nitrogen uptake in rice,and phosphorus and potassium absorption is reduced.(2)The return of organic materials in cadmium-contaminated paddy fields had limited effects on soil physicochemical properties in the first year;however,in the second year of the experiment,green manure could effectively increase soil total nitrogen and organic matter content,and rice straw could effectively increase soil nitrogen and potassium nutrients and organic matter content,among which green manure,straw return and lime application returning can increase total nitrogen by 8.2% and 11.1%,available potassium by 9.4% and 46.5%,and organic matter by 20.9% and 17.7%,respectively.The application of physical modifier lime is opposite to that of organic materials,and its improvement effect on soil physical and chemical properties in the first year is better than that in the second year.After returning green manure,straw return and lime application to the field,the activities of various soil enzymes could be increased,among which the activity of catalase increased significantly.(3)In severely cadmium-contaminated paddy soil,planting green manure to the field can effectively reduce the total cadmium content in the soil,and the two-year cumulative effect of rice straw also has a certain total cadmium reduction effect,but the effect is weaker than that of the green manure treatment;the green manure return to the field can effectively reduce soil cadmium Activity decreased by 23.7%-59.5% at the later stage of the experiment,and planting green manure and returning it to the field could reduce the effective cadmium content in the soil to the same level as the lime application.(4)The cadmium content of rice was reduced by 33.3% and 54.9% respectively after the green manure was returned to the field for two years,and the cadmium content of rice was reduced by 34.9% and 47.2% respectively by returning the rice straw to the field.In the second year of the experiment,green manure,straw return and lime applicationreduced the cadmium accumulation by 44.38% and 40.0%,respectively.Soil cadmium activity is an important factor affecting cadmium content and accumulation in rice plants.(5)Planting green manure can significantly reduce the transfer of cadmium from rice roots to rice straw and rice husk to rice;rice straw returning can mainly reduce TF rice/grass and TF rice/husk,that is,reduce cadmium from straw to rice and The transfer of rice to rice husks.Planting green manure and returning to the field can effectively increase the amount of root film,which is an important reason for increasing the cadmium content in the root and reducing the transport of cadmium to the shoot.Based on the results of the potting test of cadmium-contaminated paddy field soil green manure straw with lime application for two consecutive years,the combined return of green manure and straw can effectively improve rice yield;The activity of soil enzymes will be effectively increased after the return of green manure and straw to the field,and the total nitrogen and organic matter content of the soil will be increased in the second year of the experiment.The proportion of soil Aci-Cd and Red-Cd decreased,and it was converted into Res-Cd,which was the least harmful to rice growth,and the morphological change of cadmium in the soil was an important reason for the change of cadmium activity in the soil.Among the physicochemical properties,p H and various forms of organic matter in the soil have the greatest influence on cadmium effectiveness.The application of lime can significantly affect the cadmium activity of the soil,and the planting of green manure can also significantly reduce the cadmium activity of the soil in the later stage of the experiment,and the green manure and straw return can effectively reduce the cadmium content and accumulation of rice.Therefore,it can be considered that the combined effect of green manure,straw and lime is an effective cadmium-contaminated farmland soil treatment and rice safety production measures.