T. Purba, E. M. Harahap, C. Hanum, and R. Rahmawaty, “Land Suitability Evaluation For Paddy , Corn and Soybean in Binangalom Watershed Toba Samosir District North Sumatera”, IJSBAR, vol. 33, no. 1, pp. 131–144, Apr. 2017.