| Phytoremediation is an environmentally friendly,low-cost,safe and sustainable remediation method for heavy metals in soil in recent years,which is powered by solar energy and uses plants and their associated microorganisms to thoroughly remove pollutants from contaminated sites.However,there are still some deficiencies in practical application,such as economic cost,remediation time,plant species,surrounding climatic conditions,etc.Ideal phytoremediation should have the following characteristics:rapid growth,high biomass,high accumulation of heavy metals in easy-to-harvest and harvestable parts and certain economic value.In order to screen the cultivation mode and strengthening measures suitable for phytoremediation of mildly-to-moderately contaminated farmland,reduce and eliminate the impact of heavy metal pollution on food safety,this study selected 4 kinds of forages such as Commander chicory,Zorro chicory,Rumex and Red beet,4 kinds of oil crops such as rape,oil sunflower,peanut and sesame as well as tobacco,they were planted in the soil of mildly-to-moderately heavy metal contaminated farmland（Changfeng Village,Jiaoxi Town,Liuyang City,Hunan Province;Huangsha Village,Liling City,Zhuzhou City）,and winter forages（Commander chicory and Rumex）with high enrichment ability of heavy metals were screened through multiple mowing;2 crop rotation patterns were established with chicory and rape as winter crops and oil sunflower as spring and summer crops:chicory-oil sunflower and rape-oil sunflower.The effects of hypoaccumulator/hyperaccumulator plants on Cd remediation ability of oil sunflower with middle and later cropping in the rotation were investigated.Through film mulching/non-film mulching cultivation,the effects of different cultivation modes on phytoremediation of oil sunflower were determined.Subsequently,on the basis of film mulching cultivation,the effects of fulvic acid potassium and agricultural ammonium polyphosphate on phytoremediation of oil sunflower were explored by applying different fertilization amounts.Then,combined with mowing and film mulching,6 crops were selected to establish 2 rotation modes:chicory-tobacco-peanut,rape-oil sunflower-sesame,and the feasibility of popularizing these two rotation modes of"remediation while producing"in farmland with mild-moderate Cd pollution was discussed.The main results are as follows:（1）4 kinds of winter forages,such as Commander chicory,Zorro chicory,Rumex and Red beet,all had a good growth during mowing for 5 times.The total amount of Cd carried away by 4 kinds of forages ranged from 54.44 g ha-1to 81.12 g ha-1,among which Rumex and Commander chicory had the best Cd accumulation ability;the Pb remediation effect of Red beet was the best,and the extraction amount of Pb after mowing for 5 times reached 67.2g ha-1;the accumulation ability of Zn in Commander chicory and Rumex was also good,and the extraction amount of Zn after mowing for 5 times cutting was 4882.65 g ha-1and 4976.7g ha-1,respectively.Commander chicory and Rumex are suitable winter crops for remediation of Cd and Zn combined pollution.（2）The growth of oil sunflower was significantly inhibited by chicory,and the biomass of oil sunflower in chicory-oil sunflower rotation was 45.86%less than that of later oil sunflower in rape-oil sunflower rotation;however,in the rape-oil sunflower rotation mode,rape could promote the growth of oil sunflower in the subsequent rotation,and the total biomass of oil sunflower was 1.19 times that in CK.Both rape and chicory promoted the transport of Cd from roots to stems and increased the accumulation of Cd in stems and leaves of later oil sunflower.Later oil sunflower in rape-oil sunflower rotation not only had better Cd absorption capacity,but also had larger biomass,so the total amount of Cd extracted from later oil sunflower in chicory-oil sunflower rotation was 1.67 times that of oil sunflower after chicory.On the whole,2 rotation patterns have good remediation effects on Cd pollution in soil,but chicory planting results in obvious inhibition of the growth of oil sunflower,thus reducing the remediation effect of subsequent crops.（3）The total biomass of oil sunflower under film mulching treatment was 1.16 times of that without film mulching treatment,and the biomass of oil sunflower under film mulching treatment significantly increased.The availability of Cd,Pb,Zn and Cu increased by 23.08%,80%,1.53%and 8.45%respectively,and the content of Cd,Pb,Zn and Cu decreased by 19.42%,1.13%,2.73 and 4.98%,respectively.In addition,film mulching could significantly reduce soil p H and effectively inhibit the loss of soil organic matter（SOM）and soil cation exchange capacity（CEC）.（4）The application of fulvic acid potassium alone and two fertilizers at the same time could increase the biomass of oil sunflower,while ammonium polyphosphate alone could inhibit the growth of oil sunflower.Fertilization treatments increased the transport of Pb and Zn from oil sunflower roots to aboveground parts and decreased the bioavailability of soil Cd.The application of the two fertilizers inhibited the transport of Cd from flower disk to silique and grain.（5）After rotation for 1 year in the agricultural soil contaminated by Cd,6 crops in the two"remediation while producing"rotation patterns did not show the symptoms of heavy metal toxicity.Their biomass ranged from 10622.14 kg ha-1to 15938.67 kg ha-1,and there was a high to low order as follows:oil sunflower>rape>sesame>peanut>chicory>tobacco.The bioavailability of Cd in soil was decreased by the two rotation patterns.After rotation for 1 year,the total extraction amount of Cd in rape-oil sunflower-sesame three-season rotation pattern was 102.82 g ha-1,and the actual remediation efficiency of total Cd and available Cd was 6.8%and 8%,respectively;the total extraction amount of Cd in chicory-tobacco-peanut rotation was 85.71 g ha-1,and the actual remediation efficiency of total Cd and available Cd were 12.12%and 10.05%,respectively.The concentration of Cd in the oil extracted by n-hexane from the grains of 4 oil crops was lower than the European Union food pollution limit. |
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