WEED-CROP COMPETITION PERIOD IN THREE FINE RICE CULTIVARS UNDER DIRECT-SEEDED RICE CULTURE

Weeds are a serious biological constraint to rice production. The establishment of critical period of weed competition is central in the development of an effective weed management program. A field study was carried out to determine the critical period of weed competition in three cultivars of fine direct-seeded rice viz. Super Basmati, Basmati 2000 and Shaheen Basmati. Weeds were allowed to initially grow and compete with rice for 10, 20, 30, 40, 50 days after sowing (DAS) and a season long competition plot was also maintained. Weed flora of the experimental site comprised of Echinochloa crus-galli, E. colona, Dactyloctenium aegyptium, Leptochloa chinensis, Eleusine indica, Cyperus rotundus and C. iria and Trianthema portulacastrum, Ipomoea aquatica and Portulaca oleracea. The highest weed density was recorded between 20 and 30 DAS for all cultivars while maximum weed biomass was recorded at 50 DAS. Yield losses due to weed-crop competition were most pronounced during the period from 30 to 50 DAS. Rice yield continued to decline as the duration of weed competition increased. Weed competition beyond 20 DAS resulted in drastic reduction in the number of panicles m-2 and grains panicle-1 that accounted for lower rice yield. Broadleaved weeds represent 50% of total weed dry biomass in Super and Shaheen Basmati during early season while grasses and sedges contributed over 80% at harvest, with grasses alone contributing by ca. 65%. The period within 20 to 50 DAS appeared to be an important factor in crop weed competition in dry direct-seeded rice.