Weed management in aerobic rice systems under varying establishment methods

Aerobic rice systems, wherein the crop is established via direct-seeding in non-puddled, non-flooded fields, are among the most promising approaches for saving water and labour. However, aerobic systems are subject to much higher weed pressure than conventionally puddled transplanted rice (CPTR). Experiments were conducted for 2 years to develop effective and economical methods for managing weeds in aerobic rice grown by direct-seeding or transplanting on flat land or furrow-irrigated raised-bed systems (FIRBS). Total weed dry weight and weed density were lower with CPTR and highest with aerobic direct-seeded rice on a FIRBS (ADSB), followed by aerobic direct-seeded rice (ADSR). In terms of weight grassy weed constituted 78–96% of total weed weight in all systems of rice establishment. Loss of grain yield of rice due to weed competition ranged from 38% to 92%, being the highest in ADSB. Both weed density and dry weight were negatively correlated with rice grain yield. ADSR treatment produced yield and net economic returns similar to CPTR treatment when weeds were controlled. Pretilachlor with safener at 500 g a.i. ha−1 applied 3 days after sowing (DAS)/ days after transplanting (DAT) followed by chlorimuron+metsulfuron at 4 g a.i. ha−1 applied 21 DAS/DAT followed by hand-weeding at 35 DAS/DAT could effectively control all the weeds. The next best treatment was cyhalofop-butyl at 120 g a.i. ha−1 applied 14 DAS/DAT followed by chlorimuron+metsulfuron at 4 g a.i. ha−1 applied 21 DAS/DAT followed by hand-weeding at 35 DAS/DAT. The ADSR was as effective as conventionally puddle-transplanted rice in attaining higher rice grain yield and net returns when weeds were kept under control.