Herviyanti, ., T. B. Prasetyo, F. Ahmad, and . Darmawan. “The Properties of Humic Acids Extracted from Four Sources of Organic Matters and Their Ability to Bind Fe2+ at New Established Rice Field”. JOURNAL OF TROPICAL SOILS, vol. 15, no. 3, Apr. 2018, pp. 237-44, doi:10.5400/jts.2010.v15i3.237-244.