Data-driven precision optimization of straw and N-fertilizer input to balance SOC sequestration and stability in China’s intensive croplands

• A meta -RF-PSO framework optimizes the SOC sequestration-stability trade-off. • Straw and N input rates dominate SOC, POC, MAOC and POC/SOC responses. • Excessive straw return shows diminishing SOC gains; N effects depend on straw level. • Straw-N optimization raises SOC by 3.94% and cuts POC/SOC increase by 24.92%. Soil organic carbon (SOC) stability is crucial for sustaining long-term carbon sequestration in agricultural ecosystems. Although straw return effectively enhances SOC sequestration, it primarily elevates the active fraction—particulate organic carbon (POC)—potentially undermining SOC stability. How to balance the trade-off between SOC sequestration and stability through the synergistic management of straw and nitrogen (N)-fertilizer remains unclear. To fill this knowledge gap, we integrated 831 paired field observations from 84 studies across China and established a comprehensive framework combining meta -analysis, machine learning, and optimization algorithm. The results indicate that straw return significantly increased SOC content by 13.94% (95% confidence intervals, CIs: 12.54–15.34%), POC content by 26.36% (95% CIs: 23.40–29.54%), and mineral-associated organic carbon (MAOC) content by 10.00% (95% CIs: 8.73–11.36%), respectively. However, it also increased the POC/SOC ratio by 12.56% (95% CIs: 10.32–14.98%), confirming the inherent trade-off between SOC sequestration and stability. Random forest and restricted spline analyses revealed that N-fertilizer and straw input are key drivers with significant synergistic effects. The natural log-transformed response ratio of SOC (Ln RRSOC) failed to increase continuously with cumulative straw return, while the effect of N-fertilizer on SOC dynamics was mediated by the straw input level, producing contrasting outcomes. When straw return was divided into high and low groups based on the median value, analysis showed that under high straw return, increasing N-fertilizer enhanced both SOC sequestration (increased Ln RRSOC) and POC-to-MAOC conversion (decreased Ln RRPOC/SOC and increased Ln RRMAOC), with P < 0.05. Conversely, under low straw return, additional N-fertilizer suppressed these outcomes. Leveraging these mechanisms, we developed a nationwide synergistic management strategy using particle swarm optimization. By regionally reducing straw inputs and spatially reallocating N-fertilizer, this strategy effectively mitigates the sequestration-stability trade-off. The optimized scenario—with annual inputs of 271.33 kg N ha −1 and 9,466.33 kg straw ha −1 —increased SOC sequestration by 3.94% while significantly curbing the POC/SOC rise by 24.92% relative to baseline. These findings highlight the critical role of coordinated exogenous carbon and nitrogen inputs in securing both SOC sequestration and stability, offering a spatially tailored approach to guide sustainable agricultural management.