Spatial distribution of soil organic matter in different particle size fractions in the wind erosion region of northeastern China

• SOM predictive models for each size class explained over 75 % of the SOM variation. • The simulated mean SOM decreased with size class, except in the coarsest fraction. • The spatial distribution and area of SOM levels varied with particle size classes. Soil wind erosion is one of the major ecological and environmental issues in arid, semi-arid and partly semi-humid regions, and serves as an important driver of the migration and turnover of soil organic matter (SOM). The soil organic matter loss via wind erosion is typically calculated based on SOM of the bulk soil sample collected in the source areas, which usually remarkably deviates from the actual SOM budget. To address this discrepancy, it is imperative to examine SOM differentiation across particle size fractions and its spatial distribution in wind erosion regions. A total of 40 soil samples were collected in the wind erosion region of northeastern China and dry-sieved into eight size fractions, i.e., 0–63, 63–100, 100–150, 150–200, 200–250, 250–300, 300–400, and 400–880 μm, and SOM was measured for each fraction. The particle size-specific SOM predictive models were developed, and the spatial distribution of SOM in each fraction was simulated for the wind erosion region of northeastern China. No matter for which size fraction, the predictive model exhibited strong performance and stability based on the three key factors, i.e., SOM in bulk soil (SOM bulk ), soil clay content (CLAY) and temperature (T), which was capable of explaining over 75 % of the SOM variation. The simulated spatial mean SOM showed a general decreasing trend from the 0–63 μm to the 300–400 μm fractions, followed by a slight increase in the 400–880 μm fraction. Specifically, the area proportion of SOM larger than 30 g·kg −1 decreased markedly from 45.44 % in the 0–63 μm fraction to 16.07 % in the 300–400 μm fraction, whereas the proportion of SOM below 10 g·kg −1 increased from 8.50 % to 22.21 %. These changes were mainly distributed in western Hulunbuir City, western Xilin Gol League, and the Horqin sandy land, where soils are subject to wind erosion, characterized by low clay content and weak aggregation. In contrast, the area proportion of SOM exceeding 20 g·kg −1 rose from 37.96 % in the 300–400 μm fraction to 43.57 % in the 400–880 μm fraction. This trend was primarily spotted in the semi-humid zones, where well-developed aggregates promoted SOM accumulation. The findings provide a crucial foundation for accurate quantification of wind erosion-driven SOM loss and in-depth understanding of land degradation mechanisms in northeastern China.