Abstract:Chemical analysis and denaturing gradient gel electrophoresis (DGGE) were employed to determine the influence of long-term application of fertilizers on nitrification rates and nitrobacteria community in a calcareous purple paddy soil under rice-wheat rotations. Results showed that both pH and nitrification rates of the same soil varied substantially after long-term treatments with various fertilizers. Generally, soil amended with any fertilizers tended to reduce soil pH but increase nitrification rates compared to the control without fertilization (CK). The pH values and the nitrification rates of the soil appeared to be lower under rice rotation than those of the same soil under wheat rotation. Fertilizer amendment not only increased the soil nitrification rates but also altered the nitrobacteria community structures. As compared to the mineral fertilizer treatments, soil amendment with a combination of the mineral fertilizers with farmyard manure increased the rates of soil nitrification and the diversity of the nitrobacteria community as revealed by Unweighted Pair Group Method Clustering Analysis (UPGMA) of the DGGE banding patterns and cluster analysis of the DGGE profiles. In the soil under rice rotation, the nitrobacteria communities in soil amended with mineral nitrogen (N) or nitrogen-phosphor (NP) fertilizers was in the same cluster as that of the control (i.e.,CK). Nitrobacteria communities exposed to the fertilizer treatments with manure [manure only (M), nitrogen plus manure (NM), nitrogen and phosphor plus manure (NPM), and nitrogen, phosphor and potassium plus manure (NPKM)] fell into the second group while that exposed to the NPK，NPKMZn, NPKMMn treatments was in the third group. In the soil under wheat rotation conditions, nitrobacteria communities in M, NM, NPM, N, NP and NPKMMn fertilizer treatments were clustered into one group, those in NPK, NPKMZn and NPKMMn to another group, and those in CK as a single cluster. The study demonstrated that PCR-DGGE technique was suitable for characterizing the nitrobacteria community of the calcareous purple paddy soil under different fertilizer treatments and crop rotations.