| The cultivated land resources in china were very scarce, and the eastern coastal beach could be used as an important arable land reserve. However, amending tidal flat soil to meet the requirement of agricultural use needs heavy input of organic matter. So, cheap and high quality organic materials become an important limiting factor in the maturation of tidal flat soil. Municipal sewage sludge, which meets national standard for agricultural use, is characterized by good adhesion and high content of organic matter. Sewage sludge could accelerate the formation of organic and inorganic complexes in soils, also could promote the formation of well-structured soil. Up to date, large amount of sewage sludge has not been put to rational use in spite of. In this study, the sewage sludge, which fits the national standard for land amendment, was used as the material to investigate its potential application in tidal flat soil remediation. A field experiment with complete random design was carried out in tidal flat and the effect of sewage sludge application on soil properties and ryegrass growth was analyzed. Furthermore, the environmental impact of heavy metals in the sludge was assessed in the study. Main results obtained showed as following.(1) With the application of sludge, bulk density and particle density decreased. The quantity of soil water-stable aggregates, especially>0.25mm aggregates, increased. Soil pH decreased gradually. The content of soil organic matter, total nitrogen, total phosphorus, available nitrogen, available phosphorus and cation exchange capacity showed an upward trend. While the content of total potassium and available potassium had no significant changes. However, the application of sewage sludge increased EC and soluble salt content in the soil.(2) With the increase of sewage sludge application rate, the amount of bacteria and actinomyces in tidal flat soil showed a significant upward trend. Soil urease activity, catalase activity and peroxidase activity also increased.(3) The biomass of ryegrass plant was significantly enhanced by applying sewage sludge into tidal flat soil. With the increase of sludge application rate, total root length, root surface area, mean diameter and root volume of ryegrass increased. Furthermore, the content of N and P in the shoot and root of ryegrass was significantly higher.(4) The content of heavy metal, including Ni, Cu, Cd, Cr and Zn, in shoot and root of ryegrass seedlings increased with the increase of sewage sludge application rate. The content of heavy metals in ryegrass roots was higher than that in aboveground part. The total amount of heavy metals involved in the sludge after the application of sewage sludge, existed mainly in residual form, and effective form maintained in low levels. The environmental risk of heavy metals from the sludge could be reduced by controlling application rate. |
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