| Cadmium pollution in soil caused by wastewater irrigation,fertilizer use and waste disposal etc have attracted considerable public attention.How to control and remediate the polluted soil had become an urgent problem to be solved at present.However,to explore the distribution and mobility of cadmium in various soils as well as their relating factors would contribute to the soil heavy metals pollution prevention and remediation.Therefore,a soil-column experiment and a pot experiment were conducted respectively to investigate the Cd distribution and migration.In the soil-column,the 0-20 cm soil layer was the contaminated Henan fluvo-aquic soil selected as pollution sources,and the 20-50 cm soil layer were Heilongjiang black soil,Beijing fluvo-aquic soil and Jiangxi red soil respectively.The Multi-Species system consist of soil,earthworm and wheat named MS-3 system was set up to investigate the growth status of wheat and earthworm,the distribution and migration of cadmium,and their relating factors.The pot experiment was conducted to study the effects of biochar application on the growth and Cd uptake of the two varieties Chinese flowering cabbage,as well as the soil physical and chemical properties.The experimental results are as follows:1.Effects of MS-3 system on Cd distribution,migration and some relating factorsThe fresh and dry weight of wheat root and shoot in the soil-column with Henan fluvo-agvic soil and Beijing fluvo-agvic soil were greater than that of the two other types of soil-column.The earthworm average weight and its survival rates had no significant differences between different treatments.Earthworms mainly stayed in 0-5 cm soil layer when the soil-column planted with wheat,but they stayed in 5-15 cm soil layer when without wheat.Cadmium concentration in wheat decreased when there were earthworms in the soil-column.The Cd concentration in wheat aboveground of the three types of soil-column treated with earthworm decreased by 4.22%,10.32%and 5.88%than that without earthworm,while the Cd concentration in wheat underground part decreased by 13.48%,17.82%and 15.49%.Similarly,wheat planting could decrease the Cd concentration in earthworm,and it decreased by 10.53%,43.06%and 54.48%in the three types of soil-column planted with wheat than without wheat.Cadmium content in 0-20 cm soil layer of the three types of soil-column decreased compared with its background value,while the Cd content in 20-50 cm soil layer increased significantly.It indicated that the Cd can migrate down in the soil from the upper layer,and its migration was related to the soil types and the effects of plant and earthworm.The order of the Cd content in 0-5 cm soil layer of the four treatments in the same soil-column was:E+W<W<E<Control.The order of the Cd content in 20-50 cm soil layer of the three types was:Heilongjiang black soil<Jiangxi red soil<Beijing fluvo-agvic soil.The soil moisture in 0-20 cm soil layer increased with the depth of soil column,and its highest value was measured at 10-20 cm soil layer.In 20-50 cm soil layer,the soil moisture of Beijing fluvo-agvic soil was more than that of Jiangxi red soil and Heilongjiang black soil when they were treated with earthworms and wheat.The Henan fluvo-agvic soil in 0-20 cm layer improved the soil pH significantly in 20-50 cm layer of the three soil-column types.The soil pH of Beijing fluvo-agvic soil,Jiangxi red soil and Heilongjiang black soil after the experiment increased by 0-2.59%,0-27.95%and 0-1.13%compared with their background value 8.48,5.76 and 7.96 respectively.2.Effects of biochar derived from Pennisetum hydridu,m on Cd distribution and migration in MS-3 systemThe biochar application had no significant difference to earthworm average weight and its survival rate,but it affected the distribution of earthworms in different soil layers and resulted to increase their Cd accumulation.Compared with the treatment without biochar apllication,the number of earthworms had increased by 19.36%in 0-5 cm soil layer,but in 5-15 cm soil layer it decreased by 63.76%,and the Cd concentration of earthworms increased by 44.47%.The biochar application had no significant influence on the dry weight of wheat aboveground,but the dry weight of wheat underground part reduced by 23.64%.The biochar application had no significant influence on the Cd concentration of wheat underground part,but the Cd concentration in wheat underground part decreased by 42.37%.The biochar application could increase the soil pH and soil moisture of each soil layer.The Cd content in 0-20 cm had no significant difference,but Ca-Cd content had significant difference between them.3.Effects of Pennisetum hydridum biochar on alleviating Cd pollution in vegetable soilThe application of biochar improved soil pH and soil water content significantly,increased the organic matter content and nutrient content in soil.The organic matter contents of the three treatments applied with biochar increased by 27.99%,27.99%and 11.06%than that of the control group respectively.But the biochar had little effect on the contents of the total hydrolytic acidity and base,and cation exchange capacity(CEC).Both biochar application and cabbages planting could improve the population of soil bacteria and actinomycete,but had little effect on the soil fungi population.Applying biochar could reduce the activities of soil sucrase and neutral phosphatase to some extent,improve the soil urease activity.For instance,when Teqinchixin4 was planted after applying biochar,the soil urease activity increased by 27.47%than that of the treatment without applying biochar,and increased by 197.44%than that of the control which had neither plant nor biochar application.Applying the Pennisetum hydridum biochar could promote the growth of the two varieties of Chinese flowering cabbages,the plant height,root length and above ground biomass were increased significantly,among which plant height of Bilvcutai and Teqinchixin4 increased by 48.19%and 40.55%respectively comparing with the control group,while the aboveground fresh weight increased by 133.59%and 139.45%respectively.After Pennisetum hydridum biochar application,the Cd concentration in both aboveground and underground part of the two cabbages varieties decreased significantly,the Ca-Cd content in the soil also decreased significantly.It indicated that Pennisetum hydridum biochar can passivate Cd activity and reduce the amount of exchangeable cadmium in the soil,consequently reduce Cd accumulation in cabbages and alleviate the toxicity on cabbages from soil Cd contamination.To sum up,the results indicated that the Cd could migrate down to subsoil from the upper layer of the soil,and its migration was related to the effects of plant and earthworm.Biochar applied into the soil affected the Cd distribution and migration by affecting the soil physical and chemical properties,the effectiveness of soil cadmium,and the activities of earthworms,and therefore decreased the Cd uptake by plant from soil. |
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