Adhikary, B. H.; Vangnai, S.; Attanandana, T.; Swatdee, P.; Sripichitt, P. Growth and Nitrogen Production Rates of Azolla ( Azolla microphylla ) as Affected by Its Cultivation Methods : An Economic Perspective in Rice Cultivation in Thailand. Agr. Nat. Resour. 1997, 31, 134-140.