[Effects of long-term fertilization on soil fertility in yellow fluvo-aquic soil]

Based on the long-term field fertilization experiment in yellow fluvo-aquic soil, this study selected 2 types of soil physical, 8 items of soil chemical, and 5 soil biological properties for principal component-cluster analysis to valuate comprehensively effects of long-term fertilization on soil fertility. Results showed that significant differences of soil properties were found among the fertilization treatments. Compared with no organic manure treatment (NPK), all treatments of organic manure (M) or its combination with inorganic fertilizers (MN, MNP, MNPK) significantly reduced soil bulk density, and increased soil total porosity, the contents of soil organic carbon, total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus, microbial biomass, and activities of catalase, urease, alkaline phosphatase and invertase. Two principal components that could reflect 85.5% of the original information quantity without losing any original variables were extracted from the initial 15 indices. Within the primary group of principal components, bulk density, total porosity, organic matter, total nitrogen, alkali-hydrolyzable nitrogen, total phosphorous, available phosphorus, available potassium,microbial biomass, catalase, urease, alkaline phosphatase and inver-tase were the major contributors, while among the secondary group of principal components, total potassium and pH were the major ones. Hierarchical cluster analysis of the new indices extracted based on scores of the two principal components revealed the effects of different patterns of long-term fertilization displayed an order of MNPK＞MNP＞M, MN＞NPK＞N, NP＞CK. In conclusion, organic fertilizer has the positive effect on improving soil fertility, and combined application of organic and N, P, K fertilizer is the best fertilizing model.