Soil degradation (SD), primarily driven by erosion, poses a significant threat to agricultural productivity, ecosystem resilience, and long-term food security in semi-arid regions. This study develops an integrated framework to assess the intensity, spatial distribution, and erosion susceptibility of SD across northwestern Iran. A total of 592 soil samples were collected from 393 farmlands and 199 grasslands. The Soil Health Index (SHI) was calculated using a Minimum Data Set (MDS) approach to select the most representative physicochemical indicators of soil functionality. The 90th percentile of SHI values from grasslands was used as a reference for near-natural soil conditions, enabling quantification of degradation severity in agricultural lands. Machine learning models, including Random Forest (RF), Artificial Neural Network (ANN), and Support Vector Machine (SVM), were employed to predict spatial patterns of SD. Results showed that Inceptisols exhibited the highest degradation (mean SD = 0.353 ± 0.040), whereas Mollisols were the least degraded (mean SD = 0.199 ± 0.018), reflecting variations in soil organic carbon (SOC), bulk density (BD), and erosion susceptibility. RF outperformed other models (R² = 0.81, RMSE = 0.064), and feature importance analysis identified vegetation indices (NDVI, SAVI) and topographic factors (slope, LS-factor, TWI) as the key determinants of SD. Cold spots with relatively stable soil conditions were observed in northern and northeastern regions. This integrated approach provides a robust basis for mapping erosion-sensitive soils and designing evidence-based conservation strategies, supporting sustainable management of semi-arid agricultural lands.
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