Responses of Corn Yield, Soil Microorganisms, and Labile Organic Carbon Fractions Under Integrated Straw Return and Tillage Practices in Black Soil

In Northeast China, due to long-term, high-intensity continuous cultivation of black soil, the practice of “overuse with insufficient nurturing” has led to severe degradation of the black soil. Straw return is a crucial strategy for enhancing soil organic matter (SOM). However, the mechanism of combing straw return with different tillage methods on black soil microbial community structure and soil organic carbon (SOC) fractions remains unclear. A field experiment was conducted in black soil using four tillage treatments: conventional tillage without straw return (CK), no tillage with straw incorporation (NTS), rotary tillage with straw incorporation (RTS), and deep tillage with straw incorporation (PTS). Corn yield and the contents and fractions of SOC were measured, whereas the microbial structure at different soil depths was assessed by high-throughput sequencing technology. Meanwhile, the correlations between microbial diversity, changes in SOC fractions, and corn yield were analyzed. As a result, the straw return treatments significantly increased the contents of SOC in the 0–20 cm soil layer (up to 19.82 g kg−1 under RTS) and its labile fractions, enhanced soil microbial diversity (with a 7.03–25.14% increase in the Bacterial Chao1 index), and optimized the microbial community structure. Fungal diversity under PTS was the most prominent in the 20–40 cm depth. Correlation analysis indicated that the active SOC fractions and microbial diversity jointly explain the yield variation. The conclusions of this study will provide a theoretical foundation for developing scientifically sound straw return strategies in agricultural production.