Purwanto, Setiyo, et al. “Characteristics of Ultisols Derived from Basaltic Andesite Materials and Their Association With Old Volcanic Landforms in Indonesia”. SAINS TANAH - Journal of Soil Science and Agroclimatology, vol. 17, no. 2, Dec. 2020, pp. 135-43, https://doi.org/10.20961/stjssa.v17i2.38301.