Potential of indigenous cyanobacteria to contribute to rice performance under different schedules of nitrogen application.

Rice, IR-28, was fertilized by urea at 48, 96, 144 or 192 kg N/ha under three application schedules: (1) complete basal application before submergence, (2) split application, basal and 30 days after transplanting, or (3) 15 and 45 days after transplanting. Plant growth, yield, N accumulation, and chemical fertilizer N-use efficiency were minimum under complete basal application. N fertilization at 15 and 45 days after transplanting was superior and formed the fastest and greatest colonization by cyanobacteria. The population profile comprised 64%Nostoc, 24%Anabaena and 8%Calothrix.Aulosira, Nodularia andTolypothrix were each less than 1% of the total heterocystous cyano-bacteria.