Abstract
Soil erosion is a major concern for the environment and natural resources leading to a serious threat to agricultural productivity and one of the major causes of land degradation in the mid-hills region of Nepal. An accurate assessment of soil erosion is needed to reduce the problem of soil loss in highly fragile mountainous areas. The present study aimed to assess spatial soil loss rate and identified risk areas and their perceived impact on agricultural productivity by using the Revised Morgan–Morgan–Finney (RMMF) model and social survey in the Rangun watershed of Dadeldhura district, Nepal. Soil erosion was assessed by using data on soil, digital elevation model, rainfall, land use, and land cover visually interpreted from multitemporal satellite images, and ILWIS 3.3 academic software was used to perform the model. A household questionnaire survey (n = 120) and focus group discussion (n = 2) in identified risk areas were carried out to understand the people’s perception towards soil erosion and its impact on agricultural productivity. The predicted average soil erosions from the forest, agriculture, and barren land were 2.7 t ha−1 yr−1, 53.73 t ha−1 yr−1, and 462.59 t ha−1 yr−1, respectively. The erosion risk area under very low to low, moderate to moderately high, and high to very high covers 92.32%, 4.96%, and 2.73%, respectively. It indicates that the rate of soil erosion was lower in forest areas, whereas it was higher in the barren land. The cropped area of the watershed has been reduced by 2.96 ha−1 yr−1, and productivity has been decreased by 0.238 t ha−1 yr−1. The impacts such as removal of topsoil (weighted mean = 4.19) and gully formation (weighted mean = 3.56) were the highest perceived factors causing productivity decline due to erosion. People perceived the impact of erosion in agricultural productivity differently ( ∗ significant at P ≤ 0.05 ). The study concluded that, comparatively, barren and agricultural lands seem more susceptible to erosion, so the long-term conservation and management investment in susceptible areas for restoration, protection, and socioeconomic support contribute significantly to land rehabilitation in the Rangun watershed.
Highlights
Land resource degradation in the Himalayan region occurs mainly due to landslide, mudslide, man-made terraces, soil loss from steep slope, and decline of forest/pasture areas [1, 2]
The research approach consists of five main steps. ese are (i) identification of hydrophysical inputs parameters of Revised Morgan–Morgan–Finney (RMMF) model, (ii) field survey and informal discussion to verify the LULC Map and collection of metrological data of the study area, (iii) application of empirical relations to calculate intermediate RMMF model inputs described by [31], (iv) application of RMMF model in ILWIS Academic 3.3 while estimating spatially distributed erosion outputs such as soil loss rate and erosion risk maps, and (v) conducting field observation and households survey through questionnaire and focus group discussion (FGD) to address the impact of erosion on crop productivity
Influence of slope can be explained by soil texture; that is, silt and clay soils are dominant towards flat areas, whereas coarse texture is dominant in very steep slope of the watershed (Figure 3(b))
Summary
Land resource degradation in the Himalayan region occurs mainly due to landslide, mudslide, man-made terraces, soil loss from steep slope, and decline of forest/pasture areas [1, 2]. Soil erosion, flood, and landslides caused by torrential rain, forest fire, slash and burn cultivation, inappropriate agriculture practices, uncontrolled grazing and overgrazing, encroachment and unplanned settlements, and so forth are the common problems of the Churia hills [4]. Soil erosion is defined as the natural phenomenon in which removal and transportation of soil material occur mainly through the action of erosive agents such as water, Applied and Environmental Soil Science wind, gravity, and human disturbances [8, 9]. Soil erosion causes negative impacts on the environment and the economy, removes organic matter and important nutrients, and prevents vegetation growth, which negatively affects overall biodiversity [12, 13]
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