| With the development of economy and urbanization,the rapid growth of urban population leads to a large amount of sewage sludge and garden waste,which brings a series of burdens to the environment.Therefore,it is urgent to find a reasonable and effective way to deal with these urban wastes.The application of sewage sludge compost as soil amendment in forest ecosystem can not only make up the loss of fertility due to tree growthand improve the soil properties to a certain extent,but also is an effective way of recycling urban wastes.In this experiment,elm plantation was used as the research area,urban sludge and garden waste were taken as the research object,three types of compost products and four level of application amount were set up,i.e.,0?CK?,1.5 kg·m-2?T1?,3 kg·m-2?T2?,and6 kg·m-2?T4?.The effects of fertilizer products and application amount on p H,electrical conductivity,total N,total P and heavy metal accumulation in soil were studied through forest land experiment,and the pollution risk of heavy metals in soil after two years was analyzed.The aim of this study is to provide technical support and theoretical basis for the application of sludge compost products in forest land.The major conclusions are as follows:1.Through the long-term monitoring of the effect of forest land fertilization,the results show that:?1?The effect of fertilization on the physical and chemical properties of soil.Application of mixed compost can effectively adjust the p H value of soil,and the effect decreases with time,and returns to the initial level before fertilization in two years.Mixed compost had strong impacts on the electrical conductivity of soil which is influenced by the application amount of in the begining of fertilization,and the effect dereases as time goes The N content in the soil changed significantly with time by increasing first and then decreasing as a whole.After two years of fertilization,the total N content in the soil was higher than that of control.The P content in the soil was less affected by fertilization,however,fertilization could supplement total P content in the soil as plants grew.?2?The effect of fertilization on the total amount of heavy metals content in soil.At the early stage of fertilization,the total amount of Cr,Mn,Cu and Zn elements in soil significantly increased with the increase of fertilization amount while the total amount of Cd,Ni and Pb element did not have obvious pattern with the increase of fertilization amount.The content of Cr,Mn,Cu,and Zn in different fertilization plots decreased as time went,and the total amount of these elements didi not exceed the screening threthold value of the national standard on soil pollution.?3?The fractions of seven heavy metal elements in soil are mainly in the form of residue,and within the application range of sludge compost in this experiment,the forms of heavy metals in the soil changed with time after application,and the activity of heavy metals in Cr,Zn and Cu increases and then deactivated after application.For the three heavy mental element,the shift of form distribution was less affected by the amount of fertilization.2.The results from fertilization effect after two years showed that:?1?The content of heavy metals in the root,stem and leaf of elm in the sample plots showed different pattern with the application amount.After fertilization,Mn,Zn,Ni and Cu were easy to accumulate in roots,Mn,Zn and Cu in stems,and Ni,Zn and Mn in leaves.?2?After two years of fertilization,the activities of four soil enzymes in the sample plots changed respectively.Among them,dehydrogenase decreased significantly with the amount of application,while no obvious pattern on urease and phosphatase showed,and no obvious effect on invertase.The application of sludge compost significantly increased SEI value,index for total soil enzyme.Compost from sludge through thermohydrolysis,as well as its mixed counterpart could effectively increase soil enzyme activity in the application range of T2,while effect of mixed compost form ordinary sludge on soil enzyme activity increased with the application amount.3.Risk of heavy metals in elm soil after applying compost products for two years.?1?The risk of heavy metals in soil increased with application amount incresement,and the risk of Cd element was higher than other elelments.When applying compost to T4 level,meidium risk of pullution occured,and other heavy metals were slight risks,but the comprehensive potential ecological risk analysis indicated that they were all slight risks.The risk code evaluation method indicated that Mn element was at high risk,Cd element was at medium risk,and other elements are at low risk or no risk.The secondary phase and primary phase ratio method suggested that all elements were in risk-free range.Therefore,we should focus on Cd and Mn elements in future monitoring. |
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