Optimal straw return strategies for enhancing SOC, crop yield, and mitigating CO2 emissions in Chinese wheat and maize systems

Straw return increases soil organic carbon, which in turn enhances soil structure and water retention capacity. Optimizing straw return strategies to mitigate growing agricultural water scarcity is critical for balancing soil health, food security, and climate resilience. However, a regional-scale consensus on the impacts of straw return on soil organic carbon, carbon dioxide emissions, and crop yield is lacking. This meta-analysis, based on 494 paired field observations from wheat and maize experiments across China, evaluated soil organic carbon, carbon dioxide emissions, and crop yield responses to straw return, alongside moderating factors and key drivers integrating climate, soil, and management variables. Results showed that straw return significantly increased average soil organic carbon content (14.03 %), crop yield (9.82 %), and carbon dioxide emissions (21.21 %) compared to no straw return, sequestering carbon while boosting yields at the cost of increased carbon emissions. For specific cropping systems, climatic zones, and soil textures, combining suitable agronomic practices effectively mitigated the adverse effects of straw return. Both random forest and structural equation modeling revealed that the key drivers regulating soil organic carbon, carbon dioxide emissions, and crop yield in response to straw return were jointly determined by climatic factors (mean annual temperature and precipitation), straw return, and nitrogen management, via their direct or indirect effects on cropping systems, soil texture, tillage, and irrigation practices. Specifically, medium-term straw return (5–10 years) combined with medium nitrogen (200–400 kg N ha−1) in wheat monoculture; no-till mulching with medium-term straw return in maize monoculture; and wheat-maize rotation with low nitrogen (100–200 kg N ha−1) in regions with 10–20°C mean annual temperature, 500–1000 mm mean annual precipitation, and medium-textured soils all exhibit greater potential for carbon sequestration, yield improvement, and emission reduction. This study provides key guidance for developing site-specific straw return optimization strategies for China's wheat and maize systems through data-driven evaluation to support sustainable staple crop production.