This study focued on alfalfa fields in the Loess hilly region as research objects， with four experimental treatments were established： no fertilization （CK）， nitrogen fertilizer alone （T1）， phosphorus fertilizer alone （T2）， and combined nitrogen-phosphorus fertilization （T3）. By examining the ecological stoichiometry of soil-microbe-extracellular enzyme systems under nitrogen and phosphorus addition， this research explored the characteristics of soil nutrient limitations and the feedback mechanisms of microbial communities to metabolic constraints. The results showed that fertilization significantly decreased soil carbon to phosphorus ratio， microbial biomass carbon to phosphorus ratio （MBC∶MBP）， microbial biomass nitrogen to phosphorus ratio （MBN∶MBP）， and enzymatic stoichiometric carbon to nitrogen ratio （EEA_C∶N）. In contrast， soil nutrient content， microbial biomass， extracellular enzyme activities， and enzymatic stoichiometric nitrogen to phosphorus ratio （EEA_N∶P） were significantly increased. Enzyme vector modeling and vector analysis indicated that long-term alfalfa cultivation led to varying degrees of carbon and phosphorus limitation in soil microorganisms. Nitrogen and phosphorus addition alleviated the microbial phosphorus limitation and increased microbial carbon use efficiency （CUE）. In conclusion， appropriate supplementation of nitrogen and phosphorus fertilizers is recommended for soils under long-term alfalfa cultivation in the Loess hill region， to mitigate nutrient limitations on soil microorganisms.

Loess hills  /  Extracellular enzymes  /  Microbial nutrient limitation  /  Carbon utilization efficiency