Effects Of Si Fertilizers And Humic Acid On The Physicochemical Properties,Enzyme Activity And Characteristics Of Heavy Metal,and Soil In Heavy Metal-Polluted Soil

In recent years,with the extensive use of pesticides and chemical fertilizers,it has brought great convenience to production and life.The serious heavy metal pollution has been caused in the soil,which has become an urgent and difficult problem in China.It has been proved that silicon fertilizer and humic acid are the effective soil amendments.There may be some mechanism of action between silicon fertilizer and humic acid,which may cause the soil properties changed and affect the remediation efficiency.In this study,Cu,Cd,Pb,Zn contaminated soil was analyzed,and the effects of applying silicon fertilizer,humic acid and their combination on soil physicochemical properties,the passivation efficiency of heavy metals and soil enzyme activity were systematically studied.The possible mechanism was discussed.The main results are as follows:Silicon fertilizer,humic acid,the addition of silicon fertilizer and humic acid to heavy metal contaminated soil significantly changed the soil physicochemical properties,including p H,electrical conductivity（EC）,organic matter（OM）,organic carbon（TOC）,nitrate nitrogen（NO₃^–-N）,ammonia nitrogen（NH₄⁺-N）.The content of EC and OM could be increased by addition of silicon fertilizers,as well as the content of NO₃^–-N on day 80.Humic acid improved p H,EC,OM,NO₃^–-N content,and raised the content of WSOC、NH₄⁺-N on day 0.Si fertilizer-humic acid enhanced p H、EC、OM content in soils,and the content of WSOC on day 0 as well as the NO₃^–-N、NH₄⁺-N on days 40 and 80 were risen.It was found that silicon fertilizer-humic acid improved soil physicochemical properties,followed by humic acid and finally was silicon fertilizer.Silicon fertilizer had little effect on the change of soil available Cd and Cu,but activated available Pb and Zn.The availability of Cd,Cu,Pb,Zn in soil was significantly decreased by applying humic acid and silicon fertilizer-humic acid.Compared with the addition of silicon fertilizer or humic acid,their combination addition had a better effect on Cu passivation.Humic acid has the best passivation effect on Cd,Zn and Pb.All the restoratives completely inactivate Zn in the soil.In general,the availability of heavy metals in soil under different remediation strategies was humic acid>silicon fertilizer-humic acid>silicon fertilizer.The available heavy metal content changed with the soil physicochemical properties induced by adding amendments.The morphology and distribution of different heavy metals in soil are different.In this experiment,Cd was mainly in the form of acid extraction state,Cu and Pb were mainly in the form of oxidation state,and Zn was fixed in the soil in the form of residue state.Silicon fertilizer could reduce the acid extraction state of Cd,Cu and Pb contents and converted them into residue state,while humic acid and silicon fertilizer-humic acid treatment can significantly reduce the acid extraction state contents of Cd,Cu,Pb and Zn in soil and convert them into residue state.The effects of various amendments on the functional enzymes engaged in the soil C,N,and P cycles were investigated.With the use of silicon fertilizer,the activities ofβ-glucosidase（BG）,β-N-acetyl glucosidase（NAG）,leucine aminopeptidase（LAP）,and acid phosphatase（AP）increased.Humic acid had little effect on soil enzyme activity.In general,the activity of soil enzyme under different remediation strategies was silicon fertilizer>silicon fertilizer-humic acid>humic acid.