Soil erosion risk assessment in Moridhal watershed of Assam, India using Universal Soil Loss Equation and GIS

Abstract

Soil erosion is one of the major factors affecting sustainability of agricultural production in watershed. The objective of this paper is to estimate soil loss using the universal soil loss equation (USLE) model and GIS and to suggest soil conservation practices in Moridhal watershed. Soil loss was estimated by USLE. In addition, measurements of randomly selected soil and water conservation structures were done at four physiographic units of watershed. The erodibility of the studied soils was assessed by computing various erodibility indices like clay ratio, silt clay ratio, modified clay ratio, dispersion ratio, erosion ratio and erosion index. The soil loss of watershed was varied from very slight to very severe (range 0.87-67.77 t ha-1 yr-1). Among the physiographic units, the soil loss in the upper piedmont plain area was moderately severe to very severe with a value varying from 19.9-67.8 t ha-1 yr-1. The dispersion ratio of the soils varied from 0.06 to 1.18. It was observed that 48.82 per cent of the total studied soil samples had dispersion ratio values above 0.15 which may be considered as erodible. The erosion ratio and erosion index of studied soils varied from varied from 0.01-0.55 and 0.03-0.71, respectively. Based on the study it was found that the soils in different physiographic units are suffering from varying degree of soil erosion. The upper piedmont plain areas of the watershed require management practices which could improve the erosion status and soil productivity. The results of soil loss obtained from the study could be effectively used by the planners, watershed managers and policy makers to formulate site specific conservation plans in order to minimize soil loss for sustaining productivity.