3. Technologies for utilizing biological nitrogen fixation in wetland rice: Potentialities,current usage,and limiting factors

Almost all types of N₂-fixing microorganisms are found in lowland rice fields. The resulting N fertility has permitted moderate but constant productivity in fields where no N fertilizer is applied. Current and potential technologies for utilizing biological N₂ fixation in lowland rice production are reviewed in terms of potential, current usage, and limiting factors.Legumes and azolla have been traditionally used as green manure in parts of Asia, permitting yields of 2–4 t/ha. To a limited extent, straw incorporation favors heterotrophic biological N₂ fixation. Recently, inoculation with blue-green algae has been claimed to increase yields by about 10%. Using non-symbiotic N₂-fixing systems is still experimental.Utilization of biological N₂ fixation as an alternative or additional N source for rice is severely limited by technological, environmental, and socioeconomical factors.