Amirrullah, J., Y. Hutapea, N. Ratmini, and A. Prabowo. “Farmer Mentoring in Determining Fertilization Dosage of Corn Plants (Zea Mays L.) Using Soil Test Equipment”. Jurnal Lahan Suboptimal : Journal of Suboptimal Lands, vol. 9, no. 1, Apr. 2020, pp. 102-8, doi:10.33230/JLSO.9.1.2020.437.