Herviyanti -, Prasetyo TB, Juniarti -, Rezki D. Activation Unproductive Coal Powder with Urea to Improve Chemical Properties of Ultisols. Int. J. Adv. Sci. Eng. Inf. Technol. [Internet]. 2017 Jun. 18 [cited 2024 Jun. 2];7(3):957-63. Available from: http://ijaseit.insightsociety.org/index.php/ijaseit/article/view/2152