| In order to fill the gaps of winter crops in phytoremediation, make the most use of polluted farmland and avoid abandoning farmland, winter crops were rotated in combination with summer crops and thus efficiency of phytoremediation was developed. The study does research on remediation potential of Cd pollution in soils according to 6 kinds of rotation modes including ryegrass-sweet sorghum, winter endive-helianthus annuus, cardamine hupingshanensis-sweet sorghum, leaf mustard-sesame, purple mustard-peanut and edible-leaf beet-spring endive. Simultaneously, the effect of different fertilization treatments on Cd accumulation of oil sunflower is investigated in this study. Ryegrass, cardamine hupingshanensis, endive, leaf mustard, purple mustard and edible-leaf beet were planted by the end of December. Endive, lactuca indica, peanut, sesame, helianthus annuus and sweet sorghum planted were planted in April, after harvesting these winter crops of edible-leaf beet, cardamine hupingshanensis, endive, leaf mustard, purple mustard and ryegrass with the purpose of studying the enrichment characteristics of these crops in low and medium concentration Cd contaminated soil as well as their seasonal and environmental adaptability. Meanwhile it's aimed to explore using the 6 kinds of rotation modes in the heavy metal polluted areas instead of traditional vegetable-rice cropping pattern.the feasibility of reclamation or remediation of heavy metal polluted farmland and different fertilization treatment feasibility of phytoremediation of heavy metal contaminated soils, in order to provide technical reference for the promotion of new crop rotation patterns in light and moderate heavy metal contaminated soil. The main conclusions of this study are as follows:The experiments of Cd accumulation and extraction capacity of different crops show that-among the 6 kinds of winter crops, endive, edible-leaf beet and Cardamine hupingshanensis have the greates ability to accumulate Cd, where Cd content of aerial part is as high as 23.76 mg.kg-1,16.44 mg.kg-1 and 15.34 mg.kg-1, respectively. Among the 6 kinds of spring and summer crops, aerial part of lactuca indica has a better accumulation ability than endive. At the first clipping, Cd enrichment coefficient was up to 11.92, and 4.74 at the forth clipping, also higher than endive, which was 3 times of endive. It illuminates the great Cd pollution remediation potential of lactuca indica. Cd accumulation ability of oil sunflower, sesame, peanut and sweet sorghum is not as good as lactuca indica and endive. As far as Cd extraction is concerned, lactuca indica and sweet sorghum have the best ability for aerial part. Oil sunflower, endive (spring and summer), endive (winter) have similar ability of Cd accumulation, which is followed by the sesame, peanut, Cardamine hupingshanensis. Accumulation ability of aerial parts of peanuts, purple mustard, mustard and ryegrass is inferior to other crops. However, the fruit of peanut is its root, which means the underground part will be collected when harvesting. Whereas the Cd accumulation of its underground part is only second to edible-leaf beet.Through experiment on remediation of Cd contaminated soil with different rotation modes, it can be concluded that-Endive-helianthus annuus has the best effect to extract Cd. Up to 2.50 mg Cd can be extracted from soil after one rotation, ryegrass-sweet sorghum rotation mode and cardamine hupingshanensis-actuca indica rotation mode also have good effect of Cd accumulation.2.46 mg and 2.32 mg Cd can be extracted from soil after one rotation, respectively. Before crops planted, the content of heavy metal Cd exceeded the background value of the soil environment regulated by the government. Nevertheless, the content of heavy metal Cd decreased after rotation modes of this experiment. Among them, ryegrass-sweet sorghum has higher soil remediation efficiency, followed by beet-endive mode, ardamine hupingshanensis-actuca indica mode and endive-helianthus annuus mode. Each crop rotation model can create a certain economic benefit.Through experiment on effect of different fertilizers on accumulation of Cd to helianthus annus, the conclusion can be drawn:For mature helianthus annus, the Cd content in root is obviously higher than a growing helianthus annus, which means that Cd generally moves to the root in the experiment. Fertilization treatment doesn't have much impact on root of helianthus annus during mature period. With different treatments, Cd contents in root are almost the same, which are commonly above 10mg.kg-1. Cd accumulation effects of aerial part of helianthus annus are obviously different with different fertilization treatments. Among them, calcium magnesium phosphate fertilizer with KNO3 has the best effect to improve Cd accmultion. When nitrogen content is 100 mg.kg-1, the contents in leaves and stems are higher than other fertilizer treatments. Through (NH4)2SO4 with KH2PO4 treatment, Cd accumulation ability of helianthus annus is decent. When nitrogen content is 200 mg.kg-1, leaf has the best effect to accumulate Cd and Cd content is up to 5.98 mg.kg-1. Through KH2PO4 with Ca(NO3)2 treatment, the Cd accumulation effect of helianthus annus is worse than other treatments. Cd contents in mature helianthus annus fruit with different fertilizer treatments are all lower than in seeds in rotation modes. It means fertilizer treatment can strengthen Cd accumulation for mature helianthus annus root while not increase Cd content in fruit. |
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