Spatiotemporal Patterns and Determinants of Soil Organic Carbon Density in Coastal Saline Cropland: A Case Study of the Yellow River Delta, China

ABSTRACT Coastal saline croplands play a crucial role in sustaining food production and carbon sequestration. However, their soil carbon sequestration dynamics and its key factors remain insufficiently understood under the combined pressures of climate change and human activities. Using the Yellow River Delta as a representative case, this study used soil organic carbon density (SOCD, kg·m −2 ) as an indicator to evaluate soil carbon storage from 2009 to 2022. Correlation analysis and Random Forest modeling were applied to quantify the contributions of environmental (climatic and edaphic) and anthropogenic (cropping system) factors to SOCD. Results showed that SOCD ranged from 1.79 to 2.94 kg·m −2 , with a significant upward trend of 0.07 kg·m −2 year −1 . Spatially, higher SOCD values occurred in the southern and inland regions than in the northern and coastal areas. Total nitrogen showed the strongest explanatory importance for SOCD variation, followed by mean annual temperature, annual precipitation, total potassium, evapotranspiration, and wind speed. In contrast, soluble salt content exerted a negative influence on SOCD. Among different cropping systems, SOCD was highest under the double‐season upland system (2.22 kg·m −2 ), followed by paddy fields (2.00 kg·m −2 ), and lowest under the single‐season upland system (1.84 kg·m −2 ). Soil salinity also affected SOC indirectly by regulating the spatial distribution of cropping systems. These findings suggest that enhancing SOCD in coastal saline croplands may require integrated management strategies, including (1) reducing soil salinity and improving nitrogen management, and (2) optimizing cropping systems under the constraints of soil salinity and water availability.