Siti Mechram, Bambang Rahadi, Zaenal Kusuma, Soemarno. “Fast and Simultaneous Determination of Soil Nutrient Contents Using Near Infrared Technology”. International Journal of Advanced Science and Technology, Vol. 29, no. 04, June 2020, pp. 8385 -, http://sersc.org/journals/index.php/IJAST/article/view/30575.