Rahmi E, Suwardi S, Sumawinata B. Characterization of Humic Substance Extracted from Andisols, Spodosols, Peat, and Lignite. Sains Tanah J. Soil Sci. Agroclimatology. 2018;15(1):35-45. doi:10.15608/stjssa.v15i1.21622