## 5 Conclusions  
This study examined the effects of combining straw with no tillage (NT), rotary tillage (RT), and deep tillage (PT) on soil properties and corn yield in the black soil of Northeast China. All treatments positively influenced soil fertility, optimized the microbial community, and increased corn yield. Regarding the soil carbon components, all three straw return treatments elevated the contents of soil organic carbon (SOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) in the 0-20 cm and 20-40 cm soil layers. The return of straw enhanced organic matter input, facilitating the accumulation of SOC. The direct input of decomposable straw-derived carbon increased DOC pools. And the RTS and PTS treatments activated microbial activity, thereby promoting the MBC content. The enhancement of these carbon pools not only improved the soil's capacity to retain and supply nutrients, but also optimized the availability of soil nutrients, establishing a material foundation for high-yield corn. In terms of microbial ecology, RTS and PTS treatments promoted the growth and reproduction of aerobic microorganisms by increasing soil substrate supply, reducing soil compaction, and improving oxygen exchange conditions. This enhanced the diversity index of soil microorganisms at the phylum level, optimized microbial community structure, and strengthened the functional stability and nutrient cycling efficiency of the soil ecosystem.  
In conclusion, various straw return treatments enhanced soil fertility and ecological functions by regulating the SOC and its active components as well as microbial diversity, ultimately leading to an increase in corn yield. The research findings provide a scientific basis for the rational selection of straw return methods and the formulation of sustainable soil management strategies in the northeast black soil region. Future research should further investigate the long-term effects of different straw return models and their compatibility with regional climates and planting systems, thereby offering more precise technical support for the protection and efficient utilization of black soil.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15137129/s1](https://www.mdpi.com/article/10.3390/app15137129/s1)]([https://www.mdpi.com/article/10.3390/app15137129/s1](https://www.mdpi.com/article/10.3390/app15137129/s1)), Table S1: Soil physical and chemical properties in the different integrated straw return and tillage practices.  
Data Curation, Formal Analysis, Investigation, Visualization, Writing--Original Draft Preparation, and Writing--Review and Editing, L.F.; Writing--Review and Editing, G.C.; Conceptualization, Formal Analysis, Visualization, Writing--Original Draft Preparation, Funding Acquisition, Project Administration, and Writing--Review and Editing, Y.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by [National Key Research and Development Program of Chinal], grant number [2021 YFD1500105], and [Jilin Province Science and Technology Development Plan], grant number [20240203007 NC].  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflicts of interest.