| The improvement of environmental quality and soil fertility of Cd-contaminated farmland in south China is an important research subject on the cultivation of healthy soil in the fallow system integrated with soil remediation.The objectives of the present study were firstly to clarify the contribution of atmospheric deposition on soil Cd accumulation in agricultural ecosystems and the Cd uptake performance of rice shoots from simulated wet precipitation,the distribution and migration of Cd in the atmosphere-soil-plant systems was explored through based on field monitoring and a simulation research.Secondly,different degrees of Cd-contaminated soil were taken as the research object,and the Sedum plumbizincicola.and different crops with high accumulation of Cd were selected as the remediation plants to explore the main control factors that affect the efficiency of phytoremediation by combining various agronomic measures.Then,the phytoremediation and soil fertility technology of Cd contaminated soil were combined to explore the influencing factors of phytoremediation and soil fertilization efficiency comprehensively,and to integrate optimized the technology mode in fallow system integrated with soil remediation of Cd-contaminated soil.The main research results are as follows:(1)The spatial and temporal variations in Cd concentration and fluxes of atmospheric deposition were substantial variability in five rice-producing areas of the urbanized Chang-Zhu-Tan region over two years.The average Cd concentrations in atmospheric deposition at industrial and suburban areas were higher than the permitted limit of Cd given in the standards for irrigation water quality,and the annual Cd fluxes at industrial reached 61.0 g/ha,but all were ? 10.0 g/ha at rural areas.The net annual increase of atmospheric deposition on soil Cd accumulation in topsoil was 21.6-23.5 ?g/kg at industrial zrea,8.81-13.0 ?g/kg at suburban area and 2.15–3.46 ?g/kg at rural areas.Shoot Cd concentrations increased significantly when the annual Cd precipitation flux was ? 50 g/ha compared to the control with no Cd precipitation,and the concentration in the shoot was higher than that in roots of rice cultivar A159,when the annual simulated wet precipitation flux of Cd was 400 g/ha.Taking into account the results of the PA and the MSLR analysis,Cadmium in simulated precipitation solution also had positive direct effect on shoot Cd uptake.(2)Soil pH is one of the main factors affecting the efficiency of phytoremediation,when soil pH ? 6.0,the Cd content of moderately contaminated soil was decreased 35.8% to 57.4% compared to before phytoremediation;however,the Cd content with soil pH > 6.0 decreased 8.26%-12.3%.After phytoremediation,the soil Cd content of lightly contaminated soil decreased 38.4%(below the risk screening value);The Cd content of moderately contaminated decreased 44.2% and the heavily contaminated soil decreased 15.8%(The Cd content of S.plumbizincicola.could reach to 681 mg/kg).The efficiency of phytoremediation was higher in moderately and lightly Cdcontaminated,acidic farmland soil,while heavily contaminated soil or the soil with a low Cd availability are not suitable for phytoremediation.(3)There was no significant difference in the content of available Cd in soil with application of organic fertilizer compared with CK.However,the content of available Cd in soil of the second season was significantly lower than that in the first season,with a decrease of 17.6%-48.4% in low-contaminated soil and 4.50%-26.3% in highcontaminated soil.There was no significant difference in the content of available Cd in soil among planting of different green manure,while the content of available Cd in high-contaminated soil in the third season decreased 19.4%-25.3% compared with that in the first season.The soil nutrient index of the treatment with application of soluble organic fertilizer(OS)was increased 80.6% and 186% compared with CK in lowcontaminated soil and high-contaminated soil,respectively.Among the three green manures,the soil nutrient index of planting Astragalus sinicus L.was the highest,which was 0.77 and 0.95 in the low-contaminated and high-contaminated soil,respectively.In general,application of soluble organic fertilizer(OS)has the best effect on improving soil nutrient index and also the plant Cd content was increased compared with the other treatments,which could be used as one of the alternative measures for enhancedphytoremediation.(4)Fertilization and straw returning increased the efficiency of phytoremediation and the effect of soil fertilization on the pot experimental conditions.Compared with CK,the content of available Cd in soil of fertilization and straw returning was increased 0.30-1.40 times than that of CK,the Cd content in soil decreases 28.4%-61.1%,and the biomass,Cd content and Cd accumulation in S.plumbizincicola.increased significantly.Compared with CK,the soil pH of the treatments with application of organic fertilizer and straw returning increased significantly,and with a maximum increase of 0.91 units.The SOM increased with the treatments of fertilization and straw returning,compared with CK,and the treatments with rice straw and Astragalus sinicus L.returning were the highest,and the soil nutrient index(0.48-0.61)of straw returning treatment was significantly higher than that of other treatments(0.23-0.33).Based on the comprehensive analysis of phytoremediation efficiency and soil fertilization effect,it was found that S.plumbizincicola.+ straw mulching and S.plumbizincicola.+ soluble organic fertilizer were more suitable modes in fallow system integrated with soil remediation.(5)Compared with the selected soil,the soil Cd content in the two treatments with planting S.plumbizincicola.(SPOS and SPHA)decreased 10.8% and 15.7%,respectively,and their content of available Cd in soil decreased 37.1% and 34.3%,respectively,with rotation of different plant combinations.The bio-concentration factor of different part in all of the selected plants were higher than 1.00,and Cd content in oil sunflower leaves was as high as 7.41 mg/kg.The content of available Cd in soil of the treatment with planting oilseed rape was the highest,and the growth period of oilseed rape is the same with that of S.plumbizincicola.Therefore,planting patterns such as intercropping with S.plumbizincicola.+ oilseed rape,rotation with S.plumbizincicola.+ Cd high accumulation rice variety,and rotation with S.plumbizincicola.+ oil sunflower have the greatest application potential in the fallow system integrated with soil remediation.(6)On the field experimental conditions,there was no significant difference in the content of available Cd in soil among the different treatments,while the content of available Cd in soil at flowering period was significantly lower than that of at the seedling and branching period.Compared with CK,the content of Cd in soil treated with fertilization and straw returning decreased 1.39% to 13.9%,and their Cd content in S.plumbizincicola.were all increased.The soil pH at different growth period of S.plumbizincicola.were from 4.11 to 4.74,and the soil pH of treatment with chemical fertilizer was significantly lower than that of CK,while the soil pH with other fertilization was slightly higher than that of CK.The soil nutrient index with different treatments was OM>NPK>PM>CK>SM,the result indicated that the effect of fertilizer is the best in the treatment with application of soluble organic fertilizer(OM)by field experimental conditions.Therefore,S.plumbizincicola.+ soluble organic fertilizer were the best modes in the fallow system integrated with soil remediation by field experimental conditions. |
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