Improving Volcanic Soil Chemistry After the Eruption of Mt. Sinabung, North Sumatera in 2020

Volcanic activity produces pyroclastic deposits when erupted and cover the surrounding area. The minerals contained in these deposits are the source of plant nutrients. The volcanic deposits weathered, release nutrients to the environment, and improve soil chemical properties. The eruption of Mt. Sinabung in 2018 covered an area of 30, 320 ha, while in 2019 was 1, 371 ha. The study aims to investigate the status of nutrient content and the volcanic ash weathering level in 2020. There were 16 samples taken from ash deposits at various depths, with a total area of 1, 585.31 ha. Samples were analyzed to determine the total elemental composition using X-ray fluorescence (XRF) spectrometer, nutrient reserves, and weathering indices. The results showed that the total elemental composition of SiO2 is 51.51-67.51% classified as mafic (basalt) to felsic (dacite) materials, Al2O3; 15.54-23.41%, Fe2O3; 2.84-10.02% and CaO; 3.94-6.46%. Mount Sinabung's volcanic ash has a nutrient reserve capacity of MgO, CaO, P2O5, K2O, and SO3, respectively with the amount of 37, 384.17 kg/ha, 235, 794.99 kg/ha, 34, 293.12 kg/ha, 72, 357.39 kg/ha, and 70, 352.22 kg/ha. The weathering indices of volcanic ash of 2020 were determined with a value of 2.76-4.19 for Ruxton ratio and Product of Weathering Index (PWI) of 67.39-76.13, indicates the weathering rate of silicates from volcanic ash are still at initial stage and are still in the fresh condition.