Abstract: Soil samples were collected from a paddy field of red soil, treated with different rates of ammonium sulfate and incubated indoors at 15, 25 and 35℃, separately, for exploration of short-term effects of the treatments on nitrification, microbial biomass and microbial community diversity in the paddy red soil. Results show that NH₄⁺ content was not a significant factor of temperature in treatments the with same in ammonium sulfate application rate, while NO₃^- content was a significant factor of temperature in CK (control) and the Treatment Conventional with ammonium sulfate application rate (pure N 120 mg·kg^-1), but not either in the Treatments Moderate (N 600 mg·kg^-1) and high (1200 mg·kg^-1) in ammonium sulfate application rate. Nitrification rate increased significantly with rising temperature in CK and Treatment Conventional, while it was generally low in Treatments Moderate and High, and did not vary much with temperature. In the treatments incubated under the same temperature, nitrification rate declined with increasing ammonium sulfate application rate. In Treatments Moderate and High, soil microbial biomass carbon was a significant factor of ammonium sulfate application rate, and decreased with increasing of application rate (P<0.05), and in the treatments the with same in ammonium sulfate application rate, it varied with temperature, showing a decreasing order of 25℃ > 15℃ > 35℃. BIOLOG analysis showed that the AWCD, Shannon, Simpson and McIntosh indices were low in Treatments Moderate and High. Under 25℃, CK, among all the treatments, was the highest in AWCD, Shannon, Simpson and McIntosh indices, and Treatment Conventional followed. Overuse of ammonium sulfate may possibly undermine soil biological structure and function.

Key words: temperature, nitrification, BIOLOG, microbial biomass, ammonium sulfate