The Cd、Pb、Zn Form Distribution And Crop Enrichment Efficiency In The Soils Affected By Four Agricultural Planting Modes

Along with the social, scientific, technological and economic development, and the raising of human life level, the impact of human activity on the environment is also aggravating.A survey completed by the state environmental protection administration of China(SEPA) showed that soil, especially suburban soil in our country was seriously polluted by the heavy metal, and in that area there are massive agricultural land, so the remediation of farmland soil pollution is one of the biggest problems facing in the research of our country soil remediation. Our country agricultural soil pollution often shows the characters of composite pollution for mild, how to realize the repairment of composite pollution of agricultural soil in the premise of guarantee the normal production of farmland is one of the urgent problems needed to be solved in the remediation of soil pollution.Therefore, this paper take the WuTongQiao district, which lie on the minjiang river downstream, as the research site on the basis of existing theory and technology of phytoremediation of the contaminated soil.The goal of this research is to use the four kinds of agricultural planting mode(Ml:corn+ginger-cabbage;M2:corn-mustard; M3:rice-fallow;M4:ginger-scallion-lettuce;), composed of local existing corps, to repair the heavy metal contaminated agricultural soil by their fixed, extraction, accumulation, volatile effects of heavy metals in soil in the premise of not change the cultivated land use.The content change, distribution proportion of Cd、P、Zn in the crop-soil system, the heavy metal distribution proportion of each part of crop organizations, coefficient of concentration, the safety of edible parts of crop and its correlations to the forms of heavy metal in the soil, and the impact on the form proportion and distribution of heavy metal in the soil resulted by this are analyzed under different agricultural planting modes.The further aim of this paper is to sift a good crop combination which has a better repair effects, ecological benefits and economic benefits in a certain intensity of heavy metal pollution, looking for a effective repair way of heavy metal polluted soil, and provide a effective reference for the management of heavy metal polluted farmland soil in our country. The results were as follows.1. The results that the content of heavy metals in the soil were reduced under reasonable guidance of agricultural planting mode were verified, and the M1has the most significant effect of reducing the content of Cd in the Cd、Pb polluted faimland soil;To reduce the content of Cd in the soil which has a higher Cd content, the M3has the most ideal effect;Compared with other modes, M4has a better effect in seriously Cd, Pb, Zn composite polluted soil, especially in the reduce of Pb, Zn content.2.The content of water soluble state, exchangeable speciation, carbonate combination state of Cd and Zn, which were most sensitive to plants absorption reported by some studies, were all reduced significantly in the M2, and these were true in the M1, but the content of Fe-Mn oxide combination state Cd and Pb were significantly increased in M2; The content of organic combination state and sulphate Zn were increased significantly in the M4, and this provide a certain guidance for preventing or delaying the migration of heavy metal to crops by controlling the heavy metal forms. 3.The content of Cd, Pb, Zn in the edible part of Gramineous crops(corn and rice) were much lower than root-food crops(ginger) and vegetable(cabbage, mustard, Scal-lion, lettuce);The migration rate of Cd, Pb, Zn from root to edible part were all higher in cabbage, and it was84.49%,92.04%and153.06%respectively, so it’s better to avoid planting cabbage in Cd, Pb, Zn composite polluted soil;The migration rate of Pb, Zn from root to edible part were also higher in mustard, so choosing the planting varieties when panlting in the mild pollution soil should pay enough attention.4.The enrichment coefficients of crop root were all higher than100%in addition to ginger, and it was higher in rice(324.37%)and corn(215.80%) compared with other crops, but the crop roots were offen not removed during the harvest process, so the heavy metal absorbed in this part was easily back to farmland system along with the decomposition of plant roots, and this was a derection in the future research.Furthermore, the enrichment coefficients of Cd and Zn in the edible part of Gramineous crops were higher than other crops, this has a positive meaning for reducing the content of heavy metal in soil through the harvest transfer, and it could be taken as a way of reducing the heavy metal in soil to be explored in the future. In addition, the exploration of follow-up processing should be strengthen, in order to prevent secondary pollution and pollution diffusion.5.Through estabilishing the correlation mode between the organs of crops especially the edible parts and the content of heavy metal and it’s forms in soil, a preliminary prediction model of the food safety of economic crops harvested in Cd, Pb, Zn polluted soil could be set up, and this will be good for the planning use of the heavy metal polluted soil, and finally achieve the goal of consideration of food security, economic benefits and the ecological benefits.