Azolla (Azolla microphylla Kaulfuss) as nitrogen source and weed suppressant in drill-seeded and transplanted lowland rice [Philippines]

Maximum biomass of azolla grown with drill-seeded rice equidistantly planted was 1,183 g/m2. This biomass was 16% lower than that of transplanted rice in the same pattern. Changing the planting pattern of rice from an equidistant to double-narrow row did not increase significantly the azolla biomass, while rice yields were reduced by 8.8% and 11.1% for drill-seeded and transplanted rice, respectively. When inoculation was done 55 days after seeding rice, the growth of azolla ranged from negative to slightly positive; the biomass produced was not effective as a nitrogen source. Nitrogen content of azolla was not affected by the treatments. Basally applied azolla resulted in rice yield equivalent to that of 14.2 kg inorganic N/ha. Basal application plus an azolla crop grown after rice, incorporated and unincorporated, produced rice yield equivalent to the application of 16.9 and 31.5 kg/ha of inorganic N1550, respectively. Postseeding application of azolla alone was not effective as a nitrogen source for drill-seeded rice. Azolla reduced total weed weight by 46.7%. The weight of Monochoria vaginalis and minor weed species were also reduced by 71.0 and 58.5%, respectively. Azolla failed to suppress the growth of Echinochloa glabrescens and Echinochloa crusgalli. Weed suppression by azolla was inferior to one hand weeding. In conjunction with butachlor, azolla reduced the weight of all weed species equivalent to one or two hand weedings. Azolla mat did not affect tillering capacity, growth and yield of transplanted rice provided that the mat was not allowed to float above the rice plants. When inoculated immediately after pesticide application, azolla was susceptible to oxadiazon, butachlor and thiobencarb, but not to 2,4-D and triphenyltin hydroxide (snail killer). The five pesticides did not affect azolla biomass when inoculation was delayed 4 days after their applicat