Use of azolla to suppress weeds in transplanted rice.
In trials in 3 fields of transplanted irrigated rice cv. IR50 each with a different weed flora, N at 0 or 100 kg/ha was applied and plots either weeded once 21 days after transplanting (d.a.t.), twice at 15 and 30 d.a.t., or not weeded, with or without inoculation with azolla (Azolla pinnata). At rice harvest, azolla gave up to 95.3% reduction in dry wt. of Monocharia vaginalis, 93.9% of Cyperus difformis and 86.7% of Echinochloa glabrescens, with similar control of other spp., including Paspalum sp. However, azolla failed to suppress Scirpus maritimus and Echinochloa crus-galli ssp. hispidula, which increased by 0.4 and 226.4%, resp. Where weeds were suppressed, rice yields from azolla-treated plots (up to 4.6 t/ha) were comparable with those from hand-weeded plots (up to 4.5 t/ha); yields from non-weeded controls were up to 3.4 t/ha. Where weed control failed, azolla-treated plots gave similar yields to non-weeded control plots.