Pedological Controls on Soil Erodibility in High-Altitude Ultisols and Associated Soils of the Meghalaya Plateau, India

Soil erosion in the Meghalaya Plateau is a major environmental concern due to steep terrain, intense monsoonal rainfall, and the widespread practice of shifting cultivation. The present study examines the pedogenic implications of erosion in clay-illuvial soils (Ultisols) across twelve representative soil series using morphological, physical, and chemical properties. Soil erodibility indices—including critical shear stress (τc), erosion index of organic matter (EIROM), and the critical limit of organic matter (CLOM)—were calculated to assess soil susceptibility to erosion. In addition, the soil erodibility factor (K) was estimated using multiple linear regression (MLR) models incorporating these indices. The results indicated that soils under grass cover were slightly to moderately erodible, whereas soils under pine plantations and potato cultivation exhibited higher erosion risk. The average soil erodibility factor was 0.04 ± 0.02 t ha h ha⁻¹ MJ⁻¹ mm⁻¹ with a coefficient of variation of 45.17%, indicating considerable spatial variability in erosion processes. The MLR model developed using erodibility indices produced the equation: K = −0.053 − 0.246 CLOM + 0.807 τc − 0.00056 (very coarse sand, %) which showed a highly significant relationship (F = 430.33, p < 0.001, R² = 0.97). Another regression analysis revealed a strong collective influence of EIROM, τc, apparent cation exchange capacity (CEC), CEC/clay ratio, and soil structural stability index (SSI), expressed as: SSI = 0.4 EIROM + 19.6 τc + 0.04 (CEC/clay) − 73.2 K (F = 41, p < 0.001, R² = 0.78). Elevation showed a strong negative correlation with fine sand (r = −0.84**) and sand (r = −0.68*, p < 0.05), whereas silt exhibited a positive correlation (r = 0.59*, p < 0.05). K-means clustering grouped the soils into three clusters, revealing depletion of organic carbon and sand fractions in profiles with higher erodibility indices. Furthermore, exposed Bt horizons enriched in clay showed moderate structural stability (SSI = 5.49) and greater susceptibility to erosion in grassland and potato-growing soils. The study highlights the importance of developing detailed pedological datasets at the soil-series level across different agro-ecological regions to monitor variations in soil erodibility and support sustainable soil conservation and land management strategies.