| Sewage sludge ws a by-product in the wastewater treatment process, which contained a variety of mineral nutrients and rich organic matter that needs for plant growth. if be used in agriculture, it was an effective resource recycling pathway for sludge, but the higher concentration of heavy metal in sludge had become an important factor which limits sludge being used in agriculture. In this paper, basing on the long-term experiments and pot experiments,through studying from the yields ,nutrient and heavy metal content of crop (wheat, corn, rape) , the quality of vegetables and soil environment, we studyed characteristics of nutrient and heavy mental accumulation in soil and crop after long-term application of sewage sludge , analyzed the rape quality (soluble sugar, the reduced Vc) under different sludge applications, Finally,evaluated the safety of crop and soil in heavy mental content after sludge application.The main results obtained was as follows:1. In the field test: the application of sewage sludge could increase nutrient and yield of crop,the effect was less than chicken manure, waste fertilizer and straw , but near to chemical fertilizer after application of sludge for many years. In the pot experiment, the appropriate amount of sludge could significantly improve the biological production of rape, the best application rate was 50- 80g sludge / pot, equivalent to 7500 -12000 kgï¹’hm-2 .when the amount of sludge used more than 80 g/pot,the rape yield would show decreasing.2. The nitrogen and organic matter content of soil under three years of sludge treatment did not change significantly year to year.It was higher than the chemical fertilizer treatment and the control treatment, but less than fertilizer, chicken manure and straw.Available P and available K content in soil was relatively increased year by year.The content of availablb P in sludge treatment soil was less than chicken manure ,and the content of availablb K was lower than straw. 3. The certain amount of sludge could improve the vegetable qualities(reduced Vc ,soluble sugar and so on).When the sludge amount reached to 50-80g sludge / pot,the effect was better than fertilizer but less than chicken manure.4. The analysis of heavy metals in grain crops under sludge treatment displayed that: the contents of Cr,As, Zn and Ni in grain crops were increased with the application period ,while the contents of Cr and Hg were decreased , the contents of Pb and Cu were not changed.the contents of Cr,Hg, Cu and Zn content in grain crops were significantly higher than chemical fertilizer, waste fertilizer and straw, but the content of Pb was much lower than chicken manure. In addition, compared with the heavy metal content of crops in " Hygienic standards for grains" (GB2715-2005) and "Maximum leveal of contaminantsin foods " (GB2762-2005), the contents of Cd, Pb and Hg in crops were within limits and meet the safety standards.Analysis of heavy metals in different parts of plants could be drawn from the migration of heavy metals trend: In wheat, Cd, Cr, Pb, Hg, As and Ni mainly concentrated in the straw, while the two elements of Cu and Zn were mainly accumulated in the seed weight.In corn, Cd, Pb, Cu, Zn and Ni were mainly distributed in: straw> corn cob> grain, while Cr, and Hg were mainly located in: straw> grain> corn cob.5. Cd, Cr, Pb, Cu, Zn and Ni content of the rape which was dealed with sludge did not exceed the safety standards of vegetables (Internal standard -94, GB14935-94, GB14961-94, GB15201-94, GB3106-91).When the amount of sludge exceeded 80g / pot, Pb and As concent of rape showed a downward trend,but under all the sludge treatments ,the As content of rape was significantly higher than chicken manure treatment and control treatment.When the amount of sludge exceeded 50g / pot, the Cd, Pb, Zn and Ni concent of rape were significantly higher than the chemical fertilizer treatment and control treatment , and when the amount of sludge more than 100g/pot, the Hg content of rape was much higher than that of chemical treatment and control treatment.6. The Cd and Zn concent of each field soil increased year by year, while Cr, Pb and Ni content decreased.The Hg, As and Cu contents were stable.In potting soil, the Cd, Cr, Hg and Zn content of soil which was treated by sludge increased with the amount of sludge increasing.When the amount of sludge added to 80g/pot,the Cd, Cr,Pb, Hg and Zn concent of soil were obviously higher than chemical fertilizer and chicken manure. The Hg content of soil which applicated with sewage sludge for consecutive years was clearly higher than CK,chemical fertilizer,chicken manure,waste fertilizer and straw.In 2008,the Pb and Zn contents were obviously higher than that of chemical fertilizer and waste fertilizer.In 2009,the Cr concent gradually accumulated in the soil,and significantly higher than chemical fertilizer and chicken manure.In 2010,Cr concent decreased ,while Cd content increased in the soil.The Cd concent was obviously higher than chemical fertilizer treatment.In all,Hg and Cd were the important limiting factors of agricultural use of sewage sludge,so the changes of Hg and Cd should be paied attention to in the composting process,and take timely control in time.In addition, the heavy metals concents of field soil and potting soil did not exceed the limited scope of environmental quality standards (pH> 7.5, GB15618-1995).
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