Non-linear thresholds and spatial heterogeneity define the stabilizing benefits of soil organic carbon on the stability of crop productivity

Climate-induced interannual volatility in crop production poses a growing threat to global food security, underscoring the critical need to enhance agricultural resilience alongside maintaining reliable food supplies. Although soil organic carbon (SOC) sequestration is advocated as a nature-based solution for climate adaptation, quantifying its stabilizing benefits remains constrained by small-scale in-situ trials, simplistic linear assumptions and confounding environmental factors in previous studies.
Here, we integrated two decades (2001-2020) of high-resolution remote sensing data with a two-stage analytical framework to quantitatively characterize the stabilizing effect of SOC across China’s maize and wheat croplands. Vegetation indices (NIRv), Solar-Induced Chlorophyll Fluorescence (SIF), and MODIS gross primary productivity (MODIS GPP) were used as proxies for crop productivity, while their detrended interannual coefficient of variation (CV) served as a measure of stability. First, the generalized additive mixed model (GAMM) and XGBoost model are utilized in parallel to evaluate relationships between SOC content and crop productivity stability. Across model types, results consistently shows that maintaining higher SOC content in croplands is more beneficial for crop to buffer from external volatility. We observed critical thresholds of SOC content (maize: 10.2 – 13.4 g/kg; wheat: 8.6 – 9.9 g/kg), above which high SOC leads to more stable crop productivity. Furthermore, after determining the relationships, we employ causal forest double machine learning models (CF-DML) to isolate the marginal causal effect of SOC. Results indicate that increasing unit (g/kg) SOC can reduce the CV of crop productivity by 1.09% to 2.08% on average nationally. Specially, in regions with lower SOC levels, the marginal benefits of increasing SOC are more pronounced, particularly in areas characterized by lower soil structure and greater climate variability. In these environment-limited croplands, increasing SOC can play a more significant role in maintaining sustainable agriculture.
Our results emphasize SOC’s role in building resilient food systems. This improved understanding can refine the representation of soil carbon in earth system models and highlight the importance of soil carbon sequestration in croplands under climate change.