Spatiotemporal Variation Characteristics of the Soil Organic Carbon Stock in the Huaihe River Eco‐Economic Belt From the 1980s to 2020s

The Huaihe River Eco‐Economic Belt (HREEB), a vital grain‐producing region in China, contributes 11% of the nation's arable land and one‐sixth of its grain output. As an essential indicator of soil health, soil organic carbon (SOC) underpins long‐term productivity and ecological stability. However, the spatiotemporal dynamics of SOC stocks and the relative roles of climate and land management remain poorly quantified. This study investigated spatiotemporal changes in SOC stock in the HREEB (1980s–2020s), identified main SOC sequestration drivers, and proposed strategies for enhancing carbon stocks in sustainable agriculture. SOC stocks increased by 227.73 Tg over four decades, with an average sequestration rate of 220.30 kg C ha−1 year−1, indicating the region's significant carbon sink potential. Spatially, SOC stocks were higher in the south and lower in the north, with south–north SOC density differences of 0.70, 0.57, and 1.04 kg m−2 in the 1980s, 2010s, and 2020s, respectively. The soil pH, nitrogen input, mean annual temperature, and precipitation were the dominant explanatory variables, contributing 18.46%, 10.67%, 10.37%, and 8.05% to the explained variance in SOC density. Among these, soil pH and annual nitrogen fertilizer input showed highly significant negative correlations (p < 0.01), as pH regulates SOC stability through mineral interactions, microbial community composition, and enzyme activity. Nitrogen input of 0.072–0.177 Mg ha−1 accelerates SOC decomposition and contributes to carbon input via increased root exudates. Furthermore, both the mean annual precipitation and temperature were positively correlated with changes in SOC density, with the strongest association observed with precipitation (p < 0.05). Therefore, managing soil pH, optimizing nitrogen use, and adapting to climate change are vital for enhancing the region's soil carbon sink and supporting sustainable agricultural development.