Mas’ud, Rahmat Ibnu, Sugeng Triyono, Sri Waluyo, and Tamrin -. 2012. “Dissolved Phosphorus Of Phosphate Stones With Ultrasonic Waves As An Efforts”. Jurnal Teknik Pertanian Lampung (Journal of Agricultural Engineering) 1 (1). https://jurnal.fp.unila.ac.id/index.php/JTP/article/view/25.