Crop Straw Returning Drives Soil Multifunctionality: From Physical Reconstruction to Micro-Ecological Succession

Long-term intensive agriculture has contributed to soil compaction, carbon depletion, nutrient imbalances, and disruption of microbial ecological processes, collectively constraining multiple soil functions relevant to agricultural sustainability. Crop straw return is widely considered a potential strategy for alleviating these constraints. However, existing studies and reviews have often evaluated direct straw return, straw-derived biochar, and straw-based compost separately or through individual soil indicators, limiting understanding of how biomass transformation, amendment properties, and site conditions jointly shape soil responses. To address this gap, this review comparatively synthesizes the reported mechanisms, outcomes, limitations, and potential application contexts of these three strategies within a soil multifunctionality framework. The reviewed literature is characterized by substantial heterogeneity in soil type, climate, feedstock, amendment preparation, application rate, experimental duration, and management conditions; therefore, the direction, magnitude, and persistence of reported effects require context-specific interpretation. Direct straw return was often associated with changes in soil structure, labile-carbon availability, water retention, and microbial activity, although these responses varied with straw type, incorporation depth, moisture conditions, decomposition rate, and nitrogen availability. Biochar was frequently linked to carbon stabilization, sorption, nutrient retention, and pH buffering, but the magnitude of these effects varied with feedstock properties, pyrolysis conditions, application rate, soil characteristics, and climatic context. Compost was commonly associated with increases in nutrient availability and microbial activity, whereas its performance varied with maturity, raw-material composition, salinity and pathogen risks, and field management. These comparisons suggest that the three strategies should not be assumed to be functionally equivalent, although their effects may overlap and potential combinations may be beneficial under some conditions. Based on patterns identified across the reviewed literature, we synthesize an interpretive framework linking dominant soil constraints with amendment properties and targeted soil functions. This literature-derived framework is intended to organize context-dependent evidence and support adaptive straw-return management rather than provide a universal prescription. Future research should prioritize standardized soil multifunctionality indicators, long-term multi-site comparisons, and integrated assessments of agronomic benefits, carbon persistence, nutrient losses, greenhouse gas emissions, and economic feasibility.