Azolla is a free-floating water fern that fixes atmospheric nitrogen in association with nitrogen fixing blue green alga (Anabaena azollae). It is used as bio-fertilizer for wetland rice. It is known to contribute 40-60 kg N/ha per rice crop.

Azolla can be applied as green manure for rice before transplanting.  For this, Azolla is grown 15-20 days before transplanting of rice by applying 1-2 tonne fresh inoculum per ha in a well prepared field.

Rock phosphate is applied @ 62.5 kg/ha in three equal splits at an interval of seven days.  After the formation of thick mat, water is drained out and the field is ploughed for incorporating azolla.