Comparative studies on the N2-fixation by Azolla, blue-green algae and other organisms in the rice soil

Abstract

A nitrogen fixation study based on the nitrogen balance was conducted in ceramic pots in nitrogen fertilized and unfertilized soil under net house conditions. The incorporation of Azolla before and 20 days after transplating (DAT) of rice showed highest nitrogen balance and fixation in pot soil. Azolla used as basal + Azolla 20 DAT, Azolla basal + Blue-green algae (BGA) 20 DAT, BOA basal +Azolla 20 DAT, BOA basal + BOA 20 DAT, Azolla basal + BOA basal, Azolla basal + BOA basal, Azolla 20 DAT + Azolla 40 DAT showed a N2-fixation of 27,26, 22, 13, 5, 10, 17 and 4 mgN/kg soil/crop of rice respectively. The application of Azalea 20 DAT without incorporation, BOA 20 DAT without incorporation, 30 and 60 kg N/ha as urea and control (no N, no Arena and no BGA) fixed 8, 11, 5, 2 and 9 rng N/kg soil/crop respectively.In the unfertilized (without N-fertilizer) rice soils the flooded planted, flooded fallow, nonfloode.d planted and nonflooded fallow soil when exposed to light fixed an average of 46, 28, 41 and 24 mg N/kg soil/crop, respectively. These soils when covered with black cloth fixed only 20, 13, 20 and 17 mg N/kg soil/crop; respectively.