BIOLOGICAL N-2-FIXATION AND ITS MANAGEMENT IN WETLAND RICE CULTIVATION

The review summarizes the current status of the utilization of N-2-fix ing organisms as biofertilizer in rice cultivation. Heterotrophic bact eria, free-living cyanobacteria, Azolla, and legume green manures are considered with regard to their potential. for increasing yield, their current use and the prospects for their use with regard to the identi fied Limiting factors. Biological N-2 fixation has been the most effec tive system for sustaining production in low-input traditional rice cu ltivation. On the other hand, the utilisation of N-2-fixing organisms in intensified rice production encounters serious limitations. The uti lization of free-living bacteria and cyanobacteria is refrained by the ir modest potential and the non establishment of inoculated strains. A zolla and legumes used as green manures have a high potential as N sou rce, but their utilization is severely limited by socio-economic facto rs.