Machito Mihara

Application of USLE for the prediction of nutrient losses in soil erosion processes

Soil erosion in agricultural fields affects not only land productivity but also water environment down stream. Many investigations have been made for the prediction of soil erosion processes. The Universal Soil Loss Equation (USLE) has been applied broadly for the prediction of average annual soil loss from upland fields. However, there are few reports concerning the prediction of nutrient (N, P) losses based on the USLE. Thus, the objective of this study is to propose the prediction equation of nitrogen and phosphorus losses during soil erosion processes on the basis of the USLE. In order to predict total nitrogen and phosphorus losses, the coefficients for total nitrogen or phosphorus transfer are derived on the basis of results from experimental field plots. Three bare-cover USLE plots with different amounts of granular chemical fertilizer were installed in an experimental upland field. There was a tendency for the coefficient of total nitrogen or phosphorus transfer to increase with the average concentration of total nitrogen or phosphorus in the soils. It follows that the more granular chemical fertilizer applied caused a higher coefficient of total nitrogen or phosphorus transfer in the calculations. Moreover, the coefficients in heavily fertilized plots were higher than 1.0. Through this investigation, it became clear that the nutrient losses during soil erosion could be predicted on the basis of the coefficient of total nitrogen or phosphorus transfer along with other soil erosion parameters.

EVALUATION OF IMPACT OF EARTHQUAKE ON AGRICULTURE IN NEPAL BASED ON REMOTE SENSING

The big earthquake happening in April 2015 killed over 9000 people in Nepal. The effect of earthquake affected not only safety of local people but also agricultural field. Agricultural economy dominates in income of local people. Therefore, restoration of agricultural areas is required for improving life of locals. However, lack of information about agricultural areas is the main problem for local government to assess and restore damaged agricultural areas. Remote sensing was applied to access damaged agricultural field due to its advantages in observing responds of environment without temporal and spatial restriction. Accordingly, the objective of the study is to evaluate disaster risks based on data from questionnaire survey, remote sensing and geographic information system (GIS) in agricultural areas of Nepal. Firstly, we conducted questionnaire survey about thirty indicators of agriculture-related issues. Moreover, based on USLE (Universal Soil Loss Equation), soil erosion risk was compared between before and after the earthquake. To clarify the relation between soil erosion risk and land-use, land-use map was created based on Worldview-3. Finally, statistical analysis was conducted based on the collected data. From the results of field survey and analysis, it turned out that there was little damage on agricultural areas but huge damage on houses and barns in the villages in the research site. It is attributed to the vulnerable house materials. Soil erosion risk, that has been little observed in agricultural area, decreased in forest area and increased in residential area compared to the pre-earthquake time. From the statistical analysis, multi regression analysis was applied and age of house and elevation was computed as dominant factors of building damage in the research site. It is suggested that it is important to improve house materials in the villages and increase vegetation cover to prevent from further soil erosion in the research site.