Rice fields provide an ideal environment for harbouring Cyanobacteria
(blue-green algae). A number of reports are now available to indicate a wide
distributional spectrum of these organisoms under different soil and
agroclimatic conditions. There is enough evidence that these rice fields
cyanobacteria are capable of atmospheric nitrogen fixation in considerably large
quantities and to some extent the organic matters. Thus the role of nitrogen
fixing Cyanobacteria in the maintenance of the rice field soil fertility has
been well sustained and documented. There is now positive evidence for the
nitrogen fixing ability of more than 100 species of Cyanobacteria. During
growth, Cyanobacteria liberate relatively large quantities of combined nitrogen
mainly