Effects of rice-planting and long-term application of inorganic fertilizers on β-proteobacteria ammonium oxidizers diversity and nitrification were investigated in a soil derived from quaternary red clay in the Ecological Experimental Station of Red Soil,Chinese Academy of Sciences.The original soil is characterized by low pH and deficiency of available nutrients,particularly phosphorus and nitrogen.After 13 years of rice cultivation,the soil showed increase in number of DGGE bands of ammonium oxidizer 16S rDNA and a DGGE pattern different from that of the original soil with a similarity being only 61%,which illustrated variation in the community structure of the ammonium oxidizers in the soil.Besides,the research findings of the experiment on effect of long-term application of inorganic fertilizers on diversity of ammonium oxidizers in the soil with the PCR-DGGE method also showed that the treatments(NP,NPK&NK)in the experiment were quite similar to each other in 16S rDNA DGGE pattern,with a similarity being up to 73%.Both nitrification rate and nitrification potential were higher in the nitrogen fertilizer treatments than the other treatments.Stepwise regression analysis showed that nitrification rate and nitrification potential were evidently increased with the increase in urease activity.It may be presumed that application of urea increased soil hydrolysable nitrogen content,and hence urease activity and growth of nitrifying bacteria in the soil,which finally led to increase in nitrification rate and nitrification potential.