Baon, John Bako. “Use of Plant Derived Ash As Potassium Fertilizer and Its Effects on Soil Nutrient Status and Cocoa Growth”. JOURNAL OF TROPICAL SOILS 14, no. 3 (September 1, 2009): 185–193. Accessed July 19, 2025. https://journal.unila.ac.id/index.php/tropicalsoil/article/view/85.