| Multiple benefits such as economic and environmental benefits can be achieved through different planting systems which may take advantages of soil by optimizing the soil water and thermal conditions.However,the variation of soil environment qualities under different planting system is a issue deserving lots of researches.Field experiments were conducted on a medium polluted farmland with heavy metals which locates in Xiangtan and the pot experiments were carried out in lab as well the total content,available content in soil and the heavy metals(cu,zn,pb cd)quantities distribution in differet parts of rice(roots,straw,rice shell etc.)were studied on the basis of the analysis of total heavy metal concentration in paddy soil.The main results were as follows:(1)After two years of trial,the pH of pot experiment soil was higher than that of before,the organic matter decreased continuously,and the total concentration of heavy metals in winter significantly reduced.The Cd concentration in soil decreased 0.14 and 0.21 mg/kg respectively by planting green fertilizer and oilseed rape treatements,there was no significant difference in soil heavy metals of Cu,Zn,and Pb.The lab experiment results showed that the available concentration of Cd decreased by 0.11 mg/kg after planting rice,there was no significant difference in Cu and Pb of soil heavy metals,and Zn wassignificantly higher than that before experiment.The field experiment results shows that there was no significant difference of soil pH before and after the experiment.The soil fertilization slightly decreased and the total Cd concentration in soil had no significant difference after the field experiment.The soil heavy metals of Cu,Zn,Pb were significantly lower than before experiments.However,the content of available Cd concentration in soil decreased significantly in each treatment.According to field and lab experiment results,the content of available Cd in soil decreased significantly after planting green fertilizer and oilseed rape and the soil available Cd removal efficacy by planting green fertilizer was greater than planting oilseed rape.(2)The BCR results showed that,in pot experiment,the acid soluble fraction of Cd in soil was 48.3-80.8%,rice-fertilizer-rice variation coefficient is the least,the pot in the acid soluble in each growth stage were not significantly different,the range is 61.8% ~ 70%.The field experiment of acid soluble range is 59.6% ~ 72.9%,rice-blank-rice variation is the least,field experiment at seedling stage after acid soluble fraction were no significantly different,the range is62.7%~72.9%.The content of acid solble fraction of heavy metal decreased at first and then gradully remained stable.(3)The Cd bioavailability was 56.2-66.8% in the treatment of rice-fertilizer-rice which was lower than the treatment of rice-blank-rice.However,there was no significant difference between the three treatments of soil heavy metals of Cu,Pb and Cd,and Zn was significantly higher than that before the experiment.The field experiment results showed that the contcentrations of available Cd in soil after palnting rice-fertilzer-rice and rice-rape-rice were lower than that of rice-blank-rice,there was no significant difference among the three treatments of soil heavy metal Cu,and the soil heavy metals Zn and Pb were significantly increased compared with that before the experiments.(4)The pot experiments results showed that the average content of Cd was 0.2 mg/kg,0.38 mg/kg and 0.58 mg/kg after planting rice-fertilizer-rice,rice-rape-rice,rice-blank-rice.The field experiments results shows that Cd concentration in brown rice was 0.68 mg/kg and the concentration of Cd in early rice was greater than that in second rice.In addiont,the Cd concentrations in rice grown in the field were greater than that in pot.In general,the concentration of Cd in brown rice decreased significantly after planting rice-fertilizer-rice and rice-oilseed rape-rice and the effect of planting rice-fertilizer-rice was optimal. |
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