Abstract: It is of great significance to explore carbon, nitrogen, and phosphorus stoichiometry of soil microbial biomass under reduced fertilizer application combined with reasonable application of different organic fertilizers, and to clarify the balance between productivity and nutrient supply of croplands for efficient and green development of characteristic agricultural industry in Yunnan Plateau. We conducted a long-term fertilization experiment with tobacco-planted soils for nine consecutive years. There were five treatments, including no fertilizer (CK), local conventional recommended fertilizer (100% chemical fertilizer, CF₁), chemical fertilizer reduced by 20% (CF₂), chemical fertilizer reduced by 20% with organic fertilizer (OF), and with bio-organic fertilizer (BF). We analyzed the concentrations and stoichiometry of carbon, nitrogen, and phosphorus in microbial biomass of tobacco planting soil, and calculated the homeostasis index. The results showed that compared with treatment CF₁, treatments OF and BF significantly increased carbon, nitrogen and phosphorus contents in soil and microbial biomass, and decreased C∶N, C∶P and N∶P ratios in soil and microbial biomass. The internal stability indices (1/H) of microbial biomass C, N, P, C∶N, and N∶P were all greater than or equal to 0.75, indicating sensitive characteristics. The redundancy analysis showed positive correlations between microbial biomass C, N, and P and soil C, N, and P contents, and negative correlations between microbial biomass C∶N and C∶P ratio and soil C, N, and P contents, indicating that the changes of C, N, and P contents in tobacco planting soil induced by fertilizer reduction with different organic fertilizers directly led to the changes of stoichiometric ratios in microbial biomass. In conclusion, continuous applications of chemical fertilizer reduction of 20% with different organic fertilizers can improve nutrient contents of planted tobacco soils, which plays an important role in maintaining stoichiometric balance of carbon, nitrogen, and phosphorus in soil and microbial biomass and improving soil fertility.

Key words: tobacco planting soil, chemical fertilizer reduction, microbial biomass, ecological stoichiometric ratio, homeostasis