Puspita Sari, Niken, and Soetanto Abdoellah. “Effectiveness of Humic Acid Application on Growth of Coffee Seedings”. Pelita Perkebunan (a Coffee and Cocoa Research Journal) 33, no. 3 (December 31, 2017): 188—194. Accessed September 26, 2022. https://ccrjournal.com/index.php/ccrj/article/view/293.