Integrating geospatial techniques and the universal soil loss equation model to evaluate soil erosion vulnerability in the Moridhal watershed, Northeastern India

Soil erosion poses a significant challenge to the sustainability of agricultural systems, particularly in ecologically sensitive and topographically diverse regions such as the Moridhal watershed in Northeastern India. Despite increasing concerns, there is still a lack of spatially explicit studies that assess erosion vulnerability in this area. This study aims to quantify soil loss using the Universal Soil Loss Equation (USLE) integrated with Geographic Information System (GIS) techniques, while also evaluating the erodibility of soils across different physiographic units of the watershed. The analysis revealed that soil structural characteristics ranged from subangular blocky to massive, and textures varied from loamy sand to clay, with sandy loam being dominant. The total sand, very fine sand, silt, and clay content were found to be 5.1 to 86.0%, 2.2 to 39.2%, 8.0 to 46.8%, and 6.0 to 46.8%, respectively. A clear increasing trend of very fine sand and silt content was observed moving from the upper piedmont plain towards the floodplain. Organic matter content across the watershed ranged from moderate to high. The hydraulic conductivity, water holding capacity, and available water capacity were significantly varied across the watershed, i.e., between 0.11 and 6.54 cm hr⁻¹, 19.88 and 63.12%, and 1.0 and 22.5%, respectively. The soil loss values ranged from 0.87 to 67.77 t ha⁻¹ yr⁻¹, with the upper Piedmont plains exhibiting the most severe erosion (19.9–67.77 t ha⁻¹ yr⁻¹). Erodibility indices such as dispersion ratio (0.06–1.18), erosion ratio (0.01–0.55), and erosion index (0.03–0.71) revealed that nearly 49% of sampled soils are highly susceptible to erosion. The study underscores the urgent need for focused conservation interventions, particularly in the upper piedmont zone, to reduce erosion risks and improve land productivity. These findings offer a scientific basis for watershed management authorities, planners, and policymakers to develop site-specific strategies for erosion control and sustainable land management, which are critical for maintaining long-term agricultural productivity and soil health in this region.