Iskandar, I. and Irwanti, I. (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), pp. 23–28. doi:10.29244/jitl.5.1.23-28.