IskandarI. and IrwantiI. 2003. Use of Volcanic Sand as a Natural Fertilizer: Increasing Release of NutrientsUse of Volcanic Sand as a Natural Fertilizer: Increasing Release of Nutrients. Jurnal Ilmu Tanah dan Lingkungan. 5, 1 (Apr. 2003), 23-28. DOI:https://doi.org/10.29244/jitl.5.1.23-28.