Abstract:
Studies using the stable, heavy isotope of nitrogen (15N) were conducted to: (i) estimate quantitatively
nitrogen fixation by Azolla under rice field conditions and (ii) evaluate the uptake offAzolla-N and urea-N by
rice when incorporated into soil, as well as when using them in combination. While N2 fixation was
estimated by the 1SN- substrate labelling technique, uptake of N from labelled material was evaluated in
polythene lined 1m2 field microplots. Grain yield data were obtained from 4m x 5m yield plots having
corresponding treatments.Famers’ Experiments were also conducted in farmers’ fields to examine the
realization of the potentials demonstrated in research stations. Results showed that 55 to 66% Azolla-N was
derived from the atmosphere and 43 to 65% of Azolla-N was taken up by an associated rice crop. N-recovery
from Azolla was better than from urea, particularly when it was incorporated at tillering. As Azolla cover
left unincorporated among broadcast seeded rice enhanced the uptake of N from urea fertilizer. An
integrated use of Azolla with urea has the potential to reduce the use of chemical fertilizer by 50%, under
farmer’s field conditions.
