Sumihar Hutapea, Rahmad Syah, Ismail Husein, Benny Gunarso, Gusmeizal. “Soybean Growth Performances Based on Biochar and Organic Liquid Fertilizer Optimization Application”. International Journal of Advanced Science and Technology, Vol. 29, no. 08, June 2020, pp. 1139 -49, http://sersc.org/journals/index.php/IJAST/article/view/19808.