Rational application of nitrogen (N) fertilizers is an important measure to raise N fertilizer recovery rate and reduce N loss.A two-year field experiment of rice-wheat rotation was employed to study the effects of N fertilization modes including a N fertilizer reduction and an organic manure replacement on crop yield,nutrient uptake,soil enzyme activity,and number of microbes as well as diversity of microbes.The result showed that 20％ reduction of traditional N fertilizer dose of local farmers did not significantly change crop yield,N uptake,soil enzyme activity,and the number of microbes (bacteria,actinomycetes,and fungi).On the basis of 20％ reduction of N fertilizer,50％ replacement of N fertilizer by organic manure increased the activity of sucrose,protease,urease,and phosphatase by 46-62,27-89,33-46,and 35-74％,respectively,and the number of microbes,i.e.,bacteria,actinomycetes,and fungi by 36-150,11-153,and 43-56％,respectively.Further,organic fertilizer replacement had a Shannons diversity index (H) of 2.18,which was higher than that of other modes of single N fertilizer application.The results suggested that reducing N fertilizer by 20％ and applying organic manure in the experimental areas could effectively lower the production costs and significantly improve soil fertility and biological properties.