Potential of Azoiia as a biofertilizer for rice farming in Sri Lanka: Demonstrated by isotopic techniques

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.