B. Hariadi, H. Sastrohartono, A. W. Krisdiarto, S. Sukarman, S. Primananda, and T. H. Sagoro, “The Prediction of Nitrogen, Phosphate, and Potassium Contents of Oil Palm Leaf Using Hand-Held Spectrometer”, JTEP-L, vol. 13, no. 1, pp. 71–81, Jan. 2024.