The longterm fertilization experiment was carried out to analyze the effects of longterm fertilization on various active organic matters by determining concentrations of active organic matter in two soil layers(0—20 and 20—40 cm).Four treatments of no fertilizer(CK),single application of chemical fertilizers(NPK),single organic fertilizer(M),and organic and inorganic fertilizer application(MNPK)were arranged.Soil active organic matter was measured with oxidation of three level concent rations of KMnO₄,namely,33,167,and 333 mol/ L and thus three fractionations were high active organic matter(HAOM),middle active organic matter(MAOM),and active organic matter(AOM).Results showed that longterm application of organic manure or fertilizer can increase soil organic matter content,especially for organic and chemical fertilizer and single organic fertilizer treatments.Organic matter content in 0—20 cm soil layer was generally higher than that in 20—40 cm soil layer and fertilization caused an increase in organic matter concentration mainly in 0—20 cm soil layer.There were significant differences among fertilization modes,fertilizer types,and soil layers.In addition,there were significant relationships among the various active organic matters.The correlation coefficient for HAOM and MAOM was 0.819*;for HAOM and AOM,0.812*;and for MAOM and AOM,1.000**.Accordingly,MAOM and AOM were most closely connected among the three types of organic matter.