Abstract: By the method of relative density fractionation,this paper studied the dynamics of organic matter and its light and heavy fractions in a fluvoaquic soil under long-term fertilization.The results indicated under current fertilization system,the contents of soil organic matter and its light and heavy fractions were basically unchanged within 13 successive years of no fertilization, but had an increasing trend with the duration of chemical fertilizer NPK and organic manure applications,with a larger fluctuation among years and a less increment in treatment NPK.Regression analysis showed that soil organic matter and its light and heavy fractions had a linear correlation with the duration of fertilization in treatment NPK,and had a logarithm correlation in treatment organic manure.

Key words: Arbuscular Mycorrhizal Fungi (AMF), Soilborne disease, Interaction, Phenolic compounds, Induced resistance