Purwanto, Oky Dwi, Sudradjat Sudradjat, and Supijatno Supijatno. “Determination of Nitrogen Fertilizer Requirement for Four-Year-Old Oil Palm”. Asian Journal of Applied Sciences 5, no. 6 (December 16, 2017). Accessed September 26, 2022. https://ajouronline.com/index.php/AJAS/article/view/5097.