Abstract: Green manure returning is one of the main strategies of organic fertilization in cropland. External nitrogen and soil water content are important factors affecting the decomposition of green manure. An incubation experiment with two factors and three levels was conducted to investigate the effects of soil water contents (15%, 30%, 45%) and nitrogen (N) application rates (0, 60, 120 mg·kg^-1) on decomposition and N release rate of ryegrass (Lolium multiflorum Lam.) during returning into red soil. Under the same soil water content level, increased N fertilization rate did not promote the decomposition of ryegrass and inhibited the decomposition at 7-21 days, N application limited N release rate at 7-13 days after ryegrass returning. With the same N application rate, the increases of soil water content improved the decomposition rate of ryegrass and promoted N release rate during ryegrass returning. Increasing soil water content enhanced N release rate of ryegrass under ambient N condition compared to under N application in the late stage (57-91 days) of ryegrass returning. At the 91st day, the treatment with 45% water content and 60 mg·kg^-1 N application rate had the highest decomposition rate, being up to 0.889, while the treatment of 45% water content and 120 mg·kg^-1 N application rate had the highest rate of N released during ryegrass returning, being up to 0.885. The results of twoway ANOVA showed that soil water content had significant effects on the decomposition rate and N release rate of ryegrass. In conclusion, reasonable chemical N fertilization rate (60 mg·kg^-1) and soil water content (30%) could inhibit the decomposition and N release during the early stage, while increasing soil water content (45%) could accelerate decomposition and N release during the late stage, and thus improve N uptake and utilization of the succeeding crops.

Key words: fish community, functional richness, functional divergence, functional evenness, functional diversity, spatio-temporal variation.