THE IMPACTS OF MT. SEMERU VOLCANIC ASH ON THE NEARBY AGRICULTURAL LAND FERTILITY: A CASE STUDY OF APPLICATION OF BORE-HOLE AND GEOELECTRIC METHODS

Abstract

An investigation has been conducted, to assess the characteristics of two agricultural lands which exhibit different fertility, in Malang, Indonesia, due to volcanic ash from Mt. Semeru. The assessment was conducted using bore-hole sampling, and the geoelectric method. The results from the XRF analysis of bore-hole data indicate that the two lands have common dominant chemical contents, which are iron (Fe), and silicon (Si), whose concentrations range between 35% to 40% by mass. They also indicate, that at shallow depth, the land of Loc2 has a significantly higher concentration of phosphor (P) than that of Loc1, which is 2.1% compared to 1.2%, and that the concentration of Ca is higher at Loc1 than at Loc2, that is, about 13% to 10%. Other elements of much lower concentrations were also detected at both locations, such as Ti, K, and V. Geoelectric results show that the content of volcanic ash at shallow depths at Loc1 is thicker than that of Loc2. Higher phosphorus concentration obtained at Loc2 may be the cause of its better fertility. The results from the two methods show fairly good correlations, where, for instance, points with high Si concentration are well correlated with high resistivity values, while points whose contents are high in metallic elements have lower resistivity values. The geoelectric method has indicated that fertile land has lower resistivity, compared to less fertile ones. While the geoelectric method may offer less-quantitative results, however, it may play as an efficient complementary method.