Cyanobacteria and Azolla as green manure for wetland rice.

The ability of cyanobacteria to fix nitrogen, its sparse distribution in paddy fields and the amounts of N2 fixed by the algae in rice production are discussed. In addition, the manipulation of indigenous cyanobacterial populations is studied. The contribution of the aquatic fern azolla as a green manure for wetland rice is highlighted. The constraints to the growth of azolla, the amounts of N2 fixed by this aquatic plant and the recovery of fixed N by rice are discussed. Finally, the crop yield responses to azolla incorporation are also explored.