&mechanism was tried to develop and enrich soil organic matter and to sustain productivity of the ricerice cropping systems through its in-built biomass production from Sesbania rostrata as a relay crop. In order to develop such mechanism a number of field experiments were conducted with the participation of farmers during 1993 to 1996. Findings revealed that relay cropping of S. rostrata did not affect significantly the yields of aus and boro rice indicating its sustainability to fit it into the system. The relay cropping of S. rostrata could add up to 35.97 t ha-1 of green biomass to the soil depending upon treatments.'Incorporation of 15 to 17.5 t ha-1 of S. rostrata green biomass was as pood as application of 80 kg N ha -1 for rice yield. Post harvest soil analysis data indicated that 25 t ha- green biomass of S. rostrata was necessary to maintain the current status of soil organic matter.