Quantify the spatial transfer effect of carbon emissions induced by non-grain conversion of cultivated land use in China

China is witnessing a pronounced trend in non-grain conversion of cultivated land use (NGCCL), which impacts local food systems’ carbon footprint and induces carbon leakage through altering food supply chains and triggering off-site production compensation. Regrettably, few studies have systematically explored this critical issue. This study therefore developed a novel framework to examine NGCCL’s local effects and spatial spillovers on food system carbon emissions (FCE) from crop production substitution perspectives. A significant trend was first observed with both NGCCL and FCE generally increasing where NGCCL rose rapidly in the south and slightly declined in the north, while FCE exhibited an inverse spatial distribution. Empirical results indicated that a 1% increase in local NGCCL led to a 0.782% decrease in local FCE and a 1.410% increase in off-site FCE, resulting in a net 0.628% increase in national FCE, validating NGCCL’s carbon leakage effect characterized by “local emission reduction and off-site emission increase”. Mechanism tests showed that the spatial spillover of FCE from local NGCCL was primarily transmitted through increased irrigation area and agricultural mechanization in regions responsible for grain production compensation. Moreover, the cross-regional impact of NGCCL on FCE exhibited complex spatial heterogeneity, with the carbon leakage significantly higher in northern regions than in southern regions, and that in major grain-producing regions was found to be smaller than that in non-major grain-producing regions. By illuminating the hidden spatial carbon trade-offs embedded in agricultural land-use transitions, this study provides a critical empirical foundation for designing cross-regional collaborative governance strategies that reconcile China’s dual goals of food security and carbon neutrality.