Hartono, A, VlekP.L.G., A Moawad, and A Rachim. 2001. “Changes in Phosphorus Fractions on an Acidic Soil Induced by Phosphorus Fertilizer, Organic Matter and Lime”. Jurnal Ilmu Tanah Dan Lingkungan 3 (2), 1-7. https://doi.org/10.29244/jitl.3.2.1-7.