Oklima, A. M., . Sudarsono, . Iskandar, and D. T. Suryaningtyas. “Utilizing Coal Ash and Humic Substances As Soil Ameliorant on Reclaimed Post-Mining Land”. JOURNAL OF TROPICAL SOILS, vol. 19, no. 3, Oct. 2015, pp. 161-9, doi:10.5400/jts.2014.v19i3.161-169.