Bishnu Hari Ashikary, Prayoon Swatdee, Somsak Vangnai, Tasnee Attanadana, and Prapa Sripichitt, “Enhancing Effect of Nitrogen and Phosphorus on Azolla (Azolla microphylly) in Rice Production in Acid Sulphate Soil”, Agr. Nat. Resour., vol. 30, no. 4, pp. 539–546, Dec. 1996.