Objective To investigate the changes in soil microbial biomass and enzyme activities of black soil under the combined application of straw returning and biostimulants,

Methods Field experiments involving straw returning and different types of biostimulants were conducted to determine the variations in soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and related enzyme activities across different soil layers. Four treatments were designed, including straw returning alone (Straw), straw returning + enzyme (Enzyme), straw returning + yeast peptide (Amino), straw returning + enzyme + yeast peptide (SEA). Each treatment had three replicates, resulting in a total of 12 experimental plots.

Results The results indicated that compared with Straw treatment, the SEA treatment significantly increased MBC in the 0~5 cm soil layer by 48.72%. The SEA treatment led to a significant increase of 100.24% in the 5~10 cm soil layer and 52.29% in the 10~20 cm soil layer, respectively. Additionally, the SEA treatment remarkably enhanced the activities of dehydrogenase, β−glucosidase, β−N−acetylglucosaminase and alkaline phosphatase activities in all three soil layers. The Amino treatment significantly increased MBC in the 5~10 cm soil layer by 46.33%, while also causing a marked elevation in MBN content and acid/alkaline phosphatase activities. The Enzyme treatment substantially increased MBN in both the 0~5 cm and 5~10 cm soil layers.

Conclusions The combination of biostimulants and straw returning can increase soil microbial biomass and the activities of enzymes involved in carbon, nitrogen, and phosphorus turnover, thereby accelerating the transformation and cycling of soil elements and nutrients. This integrated measure serves as an effective agricultural management practice for improving the quality of black soil in Northeast China.