Sebayang, Lukas. “Efect of Palm Oil Factory Sludge Manure on the Growth and Yield of Cabbage”. Jurnal Online Pertanian Tropik 6, no. 3 (December 1, 2019): 371–374. Accessed August 4, 2025. https://idjpcr.usu.ac.id/jpt/article/view/3167.