F. S. Harahap, H. Walida, A. Rauf, I. Arman, S. Sudarijah, and S. Harahap, “Study of Soil Properties on Various Slopes in the Cultivation of 15-Year-Old People’s Rubber Plants in Janji Village, Bilah Hulu District, Labuhanbatu Regency”, ictess, vol. 1, no. 1, pp. 717-723, Jan. 2026.