ECOLOGY OF DEEP-WATER RICE-FIELDS IN BANGLADESH .6. INFLUENCE OF ENVIRONMENTAL-FACTORS ON SEASONAL-CHANGES IN THE RICE PLANT

Measurements of the biomass of deepwater rice plants at sites on the t hree major floodplains in Bangladesh (Ganges, Jamuna, Meghna) with and without fertilizer treatment were made from shortly before the arriva l of flood water (June) until it was receding (mid-October). There was usually an approximately linear increase in biomass per unit area wit h time until September, but subsequently there were marked differences in response, ranging from a continued steady increase to a sharp drop . Differences in the flood pattern were an important factor influencin g changes in biomass and productivity. Net productivity (biomass chang e) measured at different stages in growth ranged from -73 to +220 kg h a-1 d-1 in unfertilized fields and from -141 to +430 kg ha-1 d-1 in fe rtilized fields, with mean values of +130 in unfertilized and +160 kg ha-1 d-1 in fertilized fields. However, grain yield reflected the incr eased biomass in only one of four experiments.