Abstract: To explore the characteristics of rhizosphere soil microorganisms in paddy fields with different manure nitrogen (N) input ratios at different growth stages of early and late rice in double-cropping rice system, a field experiment was conducted with five different treatments: 1) 100% N of chemical fertilizer (M₁), 2) 30% N of organic matter and 70% N of chemical fertilizer (M₂), 3) 50% N of organic matter and 50% N of chemical fertilizer (M₃), 4) 100% N of organic matter (M₄), and 5) no N fertilizer input as a control (M₀). The rhizosphere soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial quotient (SQ) of the paddy fields were measured using the fumigation-extraction and chemical analysis methods. The results showed that the rhizosphere MBC, MBN, and SQ of the paddy fields at main different growth stages of early and late rice were increased by fertilization, which increased first and then decreased with the development of rice growth period, peaked at the heading stage, and reached the minimum value at the maturity stage. The effects of different fertilization treatments were in order of M₄＞M₃＞M₂＞M₁＞M₀, with no significant difference among M₂, M₃ and M₄, but being significantly higher than M₀. Therefore, the application of organic matter, and combined application of chemical fertilizer with organic matter could significantly increase the rhizosphere MBC, MBN, and SQ of the paddy fields at early and late rice growth period, while chemical fertilizer alone had little effect.

Key words: soil microbial biomass nitrogen, rice, soil microbial biomass carbon, fertilizer management, soil microbial quotient