Piya Duangpatra, Paiboon Prabuddham, and Chairerk Suwannarat. 1993. “Agronomic Effectiveness of Calcined Phosphate (Phospal-34) on Maize (Zea mays L.)”. Agriculture and Natural Resources 27 (4). Bangkok, Thailand:480-83. https://li01.tci-thaijo.org/index.php/anres/article/view/241702.