Systematic identification of factors influencing the spatial distribution of soil organic matter in croplands within the black soil region of Northeastern China across multiple scales

Cultivated soil organic matter (SOM) plays a critical role in maintaining soil health and promoting ecosystem services. However, the multi-scale influences on SOM changes in cropland and their interactions in the Black Soil Region of Northeastern China (BSR-NEC) remain unclear. Existing studies mainly focus on a single scale and lack a systematic multi-scale analysis. In this study, we systematically examined the multi-scale influences on SOM spatial variation in cropland within BSR-NEC using spatial autocorrelation analysis (SA), random forest models (RF), geodetector (GD), and structural equation modeling (SEM). We integrated multi-scale SOM spatial distribution influences across grid scale (GS), watershed scale (WS), and prefecture level city scale (PLS) to unveil significant differences in the spatial distribution of SOM in cropland across regions in BSR-NEC. The research indicated that: (1) the proportion of cropland with SOM content greater than 30 g/kg in BSR-NEC was 68.31 %, where the spatial distribution of SOM was more uniform at the watershed scale; (2) the Moran indices of the spatial distribution of SOM content all indicated that cropland SOM showed a trend of spatial concentration, with the grid scale (GS) > watershed scale (WS) > prefecture level city scale (PLS), mainly manifested in the form of "high-high (HH)" and "low-low (LL)" aggregation types; (3) at multiple scales, temperature and cropland type are always the main factors driving the changes of cropland SOM in BSR-NEC; (4) factors such as precipitation, elevation, and distance from urban centers exhibited varying impacts on SOM; moreover, interactions between any two factors typically resulted in nonlinear enhancements. By developing region-specific management strategies that target these key factors, our findings contribute to advancing precision and efficiency in cropland protection, aligning with the goals of the United Nations Sustainable Development Goals (SDG2030) to promote sustainable land use, improve soil health, and enhance ecosystem resilience.