Integration of GIS with RUSLE to estimate soil, organic matter and nutrient loss from a watershed of eastern Himalayan Terai

Abstract

Soil erosion is a major issue in the Indian Himalayan region, affecting both mountainous areas and the Terai. In the Terai, significant surface soil loss is driven by factors such as sandy soils, shallow soil depth, high rainfall, and the erosive force of young rivers. Human activities, including the conversion of forests and grasslands to croplands and settlements, along with poor agricultural practices, exacerbate the problem. This pilot-scale study aimed to quantify surface soil erosion and the loss of soil organic matter and nutrients in a watershed of the eastern Himalayan Terai region of India, utilizing the Revised Universal Soil Loss Equation (RUSLE) model on a Geographic Information System (GIS) platform. The results revealed substantial soil loss (\(\overline{x }\) = 32.0 Mg ha⁻¹ yr⁻¹), along with the removal of organic matter (\(\overline{x }\) = 0.95 Mg ha⁻¹ yr⁻¹), available nitrogen (\(\overline{x }\) = 1.49 kg ha⁻¹ yr⁻¹), available phosphorus (P₂O₅) (\(\overline{x }\) = 0.50 kg ha⁻¹ yr⁻¹), and available potassium (K₂O) (\(\overline{x }\) = 5.02 kg ha⁻¹ yr⁻¹). Ground surveys indicated that a significant portion of the local population was directly or indirectly affected by the annual loss of fertile topsoil, with farmers, agricultural workers, and tea garden owners being the most impacted. The erosion problem of Terai region remains unheard of as it does not cause direct damage like landslides. However, loss of topsoil every year declines the land productivity and curbs the agricultural financial benefit margin. The study recommends expanding soil erosion monitoring and modelling across the entire eastern Himalayan Terai region. Being a cost and time friendly reliable method, use of RUSLE on the GIS platform can be the best option for that. With updated erosion data, comprehensive management measures can be developed involving policymakers, administrators, researchers, and local communities.