Enriched Soil Organic Carbon Underpins Long-Term Stable Crop Productivity Across China's Croplands

Maintaining stable agricultural production amid intensifying climate extremes is critical for global food security. While soil organic carbon (SOC) is a widely recognized pillar of agricultural sustainability, the extent to which SOC accrual can enhance crop stability remains poorly quantified. Here, comprehensive large-scale datasets across China's maize and wheat croplands were leveraged to quantify nonlinear relationships using diverse nonparametric models. Critical SOC baselines (10.5-13.1 g kg^-1 for maize; 8.4-9.9 g kg^-1 for wheat) were identified as necessary for soils to effectively buffer crops against climatic fluctuations. Causal analysis revealed that approximately 20% of China's croplands were below these thresholds but exhibited significant marginal stabilizing effects from SOC enhancement. Specifically, in these high-gains regions, a 1 g kg^-1 increase in SOC improved crop stability by 6.2% to 11.1%, far exceeding the national average gains of 1.1% to 2.0%. Spatially, these pronounced gains were concentrated in municipalities characterized by high yields and extensive planting areas, highlighting that targeted SOC accrual in China's main breadbaskets was essential to secure food supply stability. By segmenting functional SOC ranges and spatially mapping marginal causal benefits, this study provides policymakers with quantitative evidence for targeted soil carbon management to enhance agricultural resilience.