Abstract: To explore the changes of microbial biomass and enzyme activities in black soil applied with straw returning and biostimulants, we conducted a field experiment with four treatments: straw returning (Straw), straw returning + enzyme (Enzyme), straw returning + enzyme + yeast peptide (SEA). We determine the soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and related enzyme activities in 0-5 cm, 5-10 cm and 10-20 cm soil with different applications. The results showed that compared with Straw, MBC of 0-5 cm soil was significantly increased by 48.72%, and MBN of 5-10 cm and 10-20 cm soil was increased by 100.24% and 52.29%, significantly. The dehydrogenase, β-glucosidase, β-N-acetylglucosaminase and phosphomonesterase activities of 0-5 cm, 5-10 cm and 10-20 cm soil were also significantly increased, respectively. The application of straw returning combined with enzyme and yeast peptide is an effective management model for
farmland to improve the quality of black soil in Northeast China.