Effects of deep ploughing incorporation of organic materials to field on the extracellular enzyme activities and stoichiometric characteristics in albic soil.

Deep incorporation of organic materials is an effective practice for soil improvement. We conducted a two-year experiment in typical albic soil with five treatments: conventional tillage (CT), deep tillage (DT), straw deep incorporation (DS), organic fertilizer deep incorporation (DM), and straw-organic fertilizer deep incorporation (DSM). We investigated the effects of deep incorporation of different organic materials on microbial biomass, extracellular enzyme activities, and their stoichiometric ratios in albic soil. The results showed that deep incorporation of organic materials (DS, DM, and DSM) significantly increased microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) in both the 0-15 cm and 15-35 cm soil layers, with the DSM treatment showing the strongest effect. MBC, MBN, and MBP under DSM increased by 72.8%, 61.6%, and 147.7% in the 0-15 cm soil layer, and 78.7%, 136.7%, and 248.4% in the 15-35 cm soil layer, respectively. Extracellular enzyme activities decreased significantly with increasing soil depth. The addition of organic materials significantly enhanced enzyme activities in each soil layer with DSM again exhibiting the largest promotion. The activities of C-acquiring enzyme (β-1,4-glucosidase), N-acquiring enzymes (β-1,4-N-acetylglucosaminidase and leucine aminopeptidase), and P-acquiring enzyme (acid phosphatase) under DSM increased by 11.6%, 65.3%, and 50.4% in the 0-15 cm layer, and 68.9%, 37.4%, and 31.1% in the 15-35 cm layer compared to CT, respectively. The enzyme-based vector model revealed that soil microbial communities across all layers of the albic soil were generally co-limited by carbon and phosphorus. Deep incorporation of organic materials significantly alleviated the nutrient limitation. Correlation analysis and random forest modeling further indicated that soil extracellular enzyme activities were regulated by MBC, MBP and MBN. Deep incorporation of organic materials could enhance microbial and enzymatic activities in albic soil and promote nutrient cycling, with the combined application of straw and organic fertilizer having the highest improvement.