The Properties of Humic Acids Extracted from Four Sources of Organic Matters and Their Ability to Bind Fe2+ at New Established Rice Field. j Trop. Soils [Internet]. 2018 Apr. 11 [cited 2025 Nov. 15];15(3):237-44. Available from: https://journal.unila.ac.id/index.php/tropicalsoil/article/view/101