| The increasingly serious Cd contamination in farmland soil hinders the safety of the resultant food products and poses a threat to the health of the entire ecosystem.To make use of farmland soils safely which were contaminated with moderate Cd,corresponding risk control and repair measures can be taken to ensure the quality and safety of agricultural products.Among many remediation technologies,in-situ immobilization remediation technology has the advantages of low cost and wide sources,and can ensure simultaneous remediation and production,which attracted much attention in the field of remediation of Cd pollution in farmland soils.According to the pollution characteristics of farmland soils in different regions,evaluating the remediation effect of various amendments is the key to achieve the safe production of Cd-contaminated farmland.A rice-wheat two-season experiment was conducted in a moderate Cd-contaminated farmland in Chengdu Plain that was under rice-wheat rotation.To observe the effect of remediation on different immobilization treatments on moderate Cd-contaminated farmland soils and the inhibition effect on Cd absorption by crop grains,exploring the changes in soil indicators in the two seasons at the same time,1 control treatment(CK)and 7 immobilization treatments(L:2250kg/hm~2 lime,S:11250 kg/hm~2 sepiolite,M1:2250 kg/hm~2 lime+11250 kg/hm~2 sepiolite,M2:2250 kg/hm~2 lime+300 kg/hm~2 sodium metasilicate+75 kg/hm~2 magnesium sulfate,M3:2250 kg/hm~2 lime+750 kg/hm~2 humic acid,BC:11250 kg/hm~2 straw biochar,TG:4500kg/hm~2 titanium gypsum)were set up and applied with amendments once per season.The main research results are as follows:(1)In the rice experiment,compared with CK,the soil pH and CEC increased by amendments,and the content of soil nutrients and trace elements changed on different level.In details,M1 raised the soil pH from 5.09 to 6.45,while 7 immobilization treatments had no obvious effect on soil fertility and CEC.Fe?Mn fertilizers could be applied appropriately during rice cultivation.Under immobilization treatments,Cd form in soils changed obviously from exchangeable fraction to residual fraction.Compared with CK,the proportion of exchangeable Cd in soil decreased by 3.06%~18.17%,and that of the residual one increased by 2.44%~33.81%,among which the immobilization effect of L,M1 and M2 were better than that of other treatments.The contents of Cd and Zn in soils after the immobilization exceeded the threshold refer to the"Risk control standard for soil contamination of agricultural land of soil environmental quality"(screening value),which caused by local factors,and the amendments had no obvious influence on it.Compared with CK,amendments had no obvious effect on rice yield.The Cd content in grains was generally reduced by 0.40%~30.68%,among which the immobilization effect of L,M1 and M2 were better than that of other treatments,but it did not meet the national food safety standard,which indicated that the application of tested amendments in a single season on this type of moderate Cd-contaminated farmland cannot access to safe rice production.(2)In the wheat experiment,the test amendments continued to increase the soil pH,nutrients(except TN,AK)and CEC on the basis of the rice season,and the soil trace elements in the two seasons were basically the same.Compared with CK,the tested amendments increased the soil pH and CEC,and the soil nutrient and trace element contents changed respectively.L raised the soil pH from 4.98 to 6.67,and 7 immobilization treatments had little effect on soil fertility,increasing CEC by 3.81%~17.45%.Fe,Mn,Cu,Zn and B fertilizers can be appropriately supplemented during wheat cultivation.On the basis of the rice season,the continued application of amendments further increased the extent of soil Cd conversion to stable fraction.Compared with CK,the proportion of soil exchangeable Cd decreased by 12.89%~21.22%,and that of the residual one increased by 13.01%~54.87%,L,M2 and BC showed outstanding immobilization effects.The changes of soil heavy metal contents in two seasons were small.Compared with CK,passivating agent has no obvious effect on wheat yield,but has a very significant inhibitory effect on Cd accumulation in wheat grains.The wheat grains Cd content was generally reduced by 35.63%~50.57%which reached to the national food safety standard,among which the immobilization effect of L,M2 and BC were better than that of other treatments.The extent of reducing the Cd content in crops grains by applying amendments in 2 consecutive seasons was significantly higher than that by applying amendments in a single season.(3)To sum up,on the premise of ensuring the original quality of soil,the immobilization effect of lime(L),lime+sepiolite(M1),and lime+sodium metasilicate+magnesium sulfate(M2)were outstanding in rice season,as well as the immobilization effect of lime(L),lime+sodium metasilicate+magnesium sulfate(M2)and straw biochar(BC)in wheat season.The restoration effect increases as the increasing of application times of amendments,the quality and the safe use of the soil environment has been further improved. |
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