Comparative studies on growth and N2 fixation of different isolates of Azolla pinnata in rice field

Abstract

Four isolates of Azolla pinnata from Bangkok, Bangladesh, Vietnam and India were grown in paddy fields before and after transplanting. Two tonnes of fresh Azolla inoculated 20 days before transplanting (DBT) in a fallow rice field, and 10 and 30 days after transplanting (DAT) in a transplanted rice field produced mats on the water surface 5 DBT, 25 DAT, and 45 DAT, resp. The Bangkok and Vietnam isolates showed more biomass and N2-fixation than those of the Bangladesh and Indian isolates. Growth and N2-fixation by Azolla isolates were greater in fallow fields than in planted fields. In planted fields, growth and N2 fixation were greater with the first Azolla crop at 25 DAT than with the second Azolla crop at 45 DAT. Growing three crops of Azolla once before transplanting and twice after transplanting produced 40.0 to 47.3, 36.7 to 46.3, 38.7 to 50.7, and 31.0 to 42.7 t/ha fresh biomass in the Bangkok, Bangladesh, Vietnam and Indian isolates resp., which fixed 68.4 to 84.2, 61.0 to 73.7, 64.4 to 86.5 and 41.7 to 68.3 kg N/ha, resp, depending upon the rice varieties used.